Fixes for the following compiler warnings:

Fixes for the following compiler warnings:

 - unused variable
 - unused parameter
 - assignment / argument discards qualifiers from pointer target type
 - comparison between signed and unsigned
 - too many arguments to function
 - assignment makes pointer from integer without a cast
 - incompatible pointer type
 - differ in signedness
 - implicit declaration of function
 - enumeration value not handled in switch
 - value computed is not used

Most notably, a possible segfault in the Rrd_Lastupdate() code of the TCL
bindings has been fixed.

Also, -Wundef (warn if an undefined identifier is evaluated in an #if
directive) has been removed from CFLAGS. I don't see any problem with letting
undefined identifiers evaluate to "false" in rrdtool. Keeping that option
would produce a lot of (imho unnecessary) errors which would need to be fixed
using ugly preprocessor statements like '#if defined(FOO) && FOO'.

-- Sebastian Harl

git-svn-id: svn://svn.oetiker.ch/rrdtool/trunk/program@1557 a5681a0c-68f1-0310-ab6d-d61299d08faa