inconsistent use of const

[Michael Callahan <callahan xmission com>]

I just grabbed the latest gtk+ as usual and compiled it with full
warnings on.  I get back some warnings for g_str_equal and some
other functions because they are using const in their declarations,
but the GCompareFunc(sp?) type declaration doesn't.

This brings up the question:  Do you really want to start using
const in this code?  It might become hard to make everything
const-consistent.

  Michael