Fix compilation on GCC 4.x

TeX Live supports compiling on GCC 4.5, which does not enable
C99 features (introduced in 2a2057b) when run with default settings.

This commit returns to pre-C99 syntax and adds instructions how to simulate
an old compiler locally.

Closes #65

ChangeLog

@@ -204,3 +204,5 @@ Handle forcing placement with ! (#62). Thanks to schrc3b6.
 Added option to print source information with -1 (#64). Thanks to Victor Cacciari Miraldo.
 
 (Version 2.8.8) -- UNRELEASED
+
+Fixed compilation on old compilers supported by TeX Live (#65). Thanks to Akira Kakuto and Hironobu Yamashita.

README-development.md

@@ -19,6 +19,11 @@ It is recommended that you install Valgrind and run tests using it (as it is don
 ./test.pl --valgrind
 ```
 
+Also recommended: check if compilation is not broken on oldest compilers supported by Tex Live (again, if you don't do this, it will be checked on CI):
+```
+make clean all DEFS='-std=iso9899:199409'
+```
+
 After pushing check cross-platform compilation results on commits list on GitHub or directly on [Travis CI](https://travis-ci.org/pkubowicz/opendetex).
 
 ## Releasing a new version

detex.l

@@ -732,7 +732,8 @@ Echo()
 void
 IncrLineNo()
 {
-	for (char* c=yytext; *c != '\0'; c++) {
+	char *c;
+	for (c=yytext; *c != '\0'; c++) {
 		if (*c == '\n') {
 			fFileLines[csb]++; fIsColumn0=1;
 		}