Use predefined constants for PlcStatus instead of string literals

cleanup: pylint, R1704 # (redefined-argument-from-local) Redefining argument with the local name 'Y'

cleanup: pylint, R1701 # (consider-merging-isinstance) Consider merging these isinstance calls to isinstance(CTNLDFLAGS, (str, unicode))

cleanup: pylint, E1304 # (missing-format-string-key) Missing key 'X_name' in format string dictionary

cleanup: pylint, E1300 # (bad-format-character) Unsupported format character '"' (0x22) at index 17

cleanup: pylint, W0111 # (assign-to-new-keyword) Name async will become a keyword in Python 3.7

cleanup: pylint, E1310 (bad-str-strip-call) Suspicious argument in str.strip call

Fix segmentation fault when last lines in text POUs should be highlighted

enable etherlab checks

resort enabled pylint check to move likely-most invasive changes to the end

clean etherlab: pylint, C0330 # (bad-continuation) Wrong hanging indentation before block

clean etherlab: pylint, W0612 # (unused-variable) Unused variable 'X'

clean etherlab: pylint, W1618 # (no-absolute-import) import missing `from __future__ import absolute_import`

clean etherlab: pylint,E0602 # (undefined-variable) Undefined variable 'X'

clean etherlab: pylint, E1136 # (unsubscriptable-object) Value 'X' is unsubscriptable

ignore missing MotionLibrary

to fix pylint error 'E0401 # (import-error) Unable to import 'X'

clean etherlab: pylint, E0611 # (no-name-in-module) No name 'X' in module 'Y'

clean etherlab: pylint, C0123 # (unidiomatic-typecheck) Using type() instead of isinstance() for a typecheck.

clean etherlab: pylint, W0104 # (pointless-statement) Statement seems to have no effect

clean etherlab: pylint, W0631 # (undefined-loop-variable) Using possibly undefined loop variable 'X'

clean etherlab: pylint, C1001 # (old-style-class) Old-style class defined.

clean etherlab: pylint, W0611 # (unused-import) Unused import X

clean etherlab: pylint, E0102 # (function-redefined) method already defined

clean etherlab: pylint, W0105 # (pointless-string-statement) String statement has no effect

clean etherlab: pylint,W0231 # (super-init-not-called) __init__ method from base class is not called

clean etherlab: pylint, C0412 # (ungrouped-imports) Imports from package X are not grouped

clean etherlab: pylint,W0108 # (unnecessary-lambda) Lambda may not be necessary

clean etherlab: pylint, C0411 # (wrong-import-order) standard import "import x" comes before "import y"

clean etherlab: pylint, W0404 # reimported module

check_source.sh: add E301 check to the list of selected PEP8 errors

clean etherlab: pep8, E301 expected 2 blank lines, found 1

clean etherlab: pep8, W503 line break before binary operator

clean etherlab: pep8, E266 too many leading '#' for block comment

clean etherlab: pep8, E122 continuation line missing indentation or outdented

clean etherlab: pep8, W191 indentation contains tabs

clean etherlab: pep8, E211 whitespace before '['

clean etherlab: pep8, E129 visually indented line with same indent as next logical line

clean etherlab: pep8, E127 continuation line over-indented for visual indent

clean etherlab: pep8, E129 visually indented line with same indent as next logical line

clean etherlab: pep8, W602 deprecated form of raising exception

clean etherlab: pep8, W601 .has_key() is deprecated, use 'in'

clean etherlab: pep8, E731 do not assign a lambda expression, use a def

clean etherlab: pep8, E203 whitespace before ','

clean etherlab: pep8, E712 comparison to True should be 'if cond is True:' or 'if cond:'

clean etherlab: pep8, E222 multiple spaces after operator

clean etherlab: pep8, E741 ambiguous variable name 'l'

cleanup etherlab: pep8, E306 expected 1 blank line before a nested definition, found X

cleanup etherlab: pep8, E305 expected 2 blank lines after class or function definition, found X

cleanup etherlab: pep8, E201 whitespace after '('

cleanup etherlab: pep8, E202 whitespace before ')'

cleanup etherlab: pep8, E227 missing whitespace around bitwise or shift operator

cleanup etherlab: pep8, E251 unexpected spaces around keyword / parameter equals

cleanup etherlab: pep8, E225 missing whitespace around operator

cleanup etherlab: pep8, E303 too many blank lines (2)

cleanup etherlab: pep8, E231 missing whitespace after ','

cleanup etherlab: pep8, E271 multiple spaces after keyword

cleanup etherlab: pep8, E261 at least two spaces before inline comment

cleanup etherlab: pep8, E302 expected 2 blank lines, found 1

cleanup etherlab: pep8, W293 blank line contains whitespace

cleanup etherlab: pep8, E228 missing whitespace around modulo operator

cleanup etherlab: pep8, E401 multiple imports on one line