#11 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://linuxquota.cvs.sourceforge.net/viewvc/linuxquota/quota-tools/quotacheck.h?revision=1.6&view=markup
fmtstr (function "debug")
filename (functions "v2_detect_version" and "..._buffer_file")

- http://linuxquota.cvs.sourceforge.net/viewvc/linuxquota/quota-tools/quotaops.h?revision=1.4&view=markup
name (functions "writeprivs" and "writeindividualtimes")