Add check bison version in configure.ac file.
To build correctly matiec we need bison greater or equals than 2.4 version.
Now the "configure" script is able to check if system has correctly requirements.
################
# IL operators #
################
# which are not simultaneously
# - keywords (AND, OR, NOT, MOD, XOR),
# - or standard funtion name (which by implication are also keywords)
# (AND, OR, NOT, MOD, XOR, as well as, GE, GT, LE, LT, EQ, NE, SUB, ADD, MUL, DIV)
# - or standard function block name (which by implication are also keywords)
# - invalid identifier name (&, &N)
ANDN
CAL
CALC
CALCN
CD
CLK
CU
IN
JMP
JMPC
JMPCN
LD
LDN
ORN
PT
PV
R
R1
RET
RETC
RETCN
S
S1
ST
STN
XORN
##################
# SFC qualifiers #
##################
D
DS
L
N
P
#R -> also an IL operator
#S -> also an IL operator
SD
SL
#####################
# Task initialisers #
#####################
PRIORITY
SINGLE
INTERVAL