Better identification of error location in some error messages.

Fix bug introduced in 2014/10/19, while adding support for REF() opertors -> datatype checking was not catching datatype inconsistency errors!

merge

Re-write and fix the logic of SFC action modifiers.

Correct the number given to actions in the #define's

Do not allow constant_propagation algorithm go into infinite loop when analysing code with circular references.

Do constant propagation of FBs instantiated in other FB or Programs, so that variable sized arrays can be declared in FBs too.

Do constant propagation of instantiated FBs, so that variable sized arrays can be declared in FBs too.

Let get_datatype_info_c handle variable sized arrays, even if constant folding is not yet done.

Correctly analyse external<->global var compatibility when using variable sized arrays (TODO: does not yet work for FBs!)

Add comment about bug that needs to be fixed later on.

Break constant_folding_c in two classes: constant_folding_c and constant_propagation_c

Add check whether the same constant var_external variable is initialised with two (or more) different constant values.

Change algorithm for propagating VAR_GLOBAL constant values to corresponding VAR_EXTERNAL.

Disable constant propagation again (still not working correctly)

Make support for use of variables in array size declarations a command line option (off by default)

Add debug_c::print(const_value_c) for printing of const values.

Add is_undefined() method to const_value_c

Make error message more informative.

Add comments.

Add checks for use of non constant value in subranges, and lower_limit > upper_limit.

Fix previous commit (symtable operator[] must return a reference to the stored value!)

Do constant propagation of configuration/resource variables, taking into account scope of variables.

Change dsymbtable_c -> use design pattern used by C++ standard library (STL)