r12043: It's amazing the warnings you find when compiling on a 64-bit

r12043: It's amazing the warnings you find when compiling on a 64-bit
box with gcc4 and -O6...
Fix a bunch of C99 dereferencing type-punned pointer will break
strict-aliasing rules errors. Also added prs_int32 (not uint32...)
as it's needed in one place. Find places where prs_uint32 was being
used to marshall/unmarshall a time_t (a big no no on 64-bits).
More warning fixes to come.
Thanks to Volker for nudging me to compile like this.
Jeremy.