#1 Improve const-correctness

[Markus Elfring]

Would you like to apply the advices from the article "http://en.wikipedia.org/wiki/Const-correctness" to more places in your sources?
I suggest to add the key word "const" to the type specifiers for parameters like the following.
http://extace.cvs.sourceforge.net/extace/extace/include/configfile.h?revision=1.1&view=markup
cfg, filename (function "cfg_write_file")
section, key, gfloat (function "cfg_write_float")