[krbdev.mit.edu #7095] Build system uses @localedir@ without requiring autoconf 2.60

[Greg Hudson via RT]

src/config/pre.in uses @localedir@ in the definition of KRB5_LOCALEDIR.  
This variable was added in autoconf 2.60, but we only require autoconf 
2.52 in our AC_PREREQ.

There are several choices for fixing this: we could start requiring 
autoconf 2.60, we could use $(datadir)/locale instead of @localedir@ in 
the definition of KRB_LOCALEDIR, or we could make configure.in define 
localedir for autoconf 2.5x.