Especially in error handling, and code that does a lot of other string
operations anyway the speed gain is not wort the 100+ bytes code size
of each instance of push_constant_text

This saves about 20K of code size (main pike binary), while not really
changing the speed much.

push_constant_text that seemed to be in at least pseudo-time-critical
code was kept as they were.

On a related note, push_constant_text(":") four times in a row creates
four different string variables, for obvious reasons.

Some of the remaining push_constant_text really should have a
module/file local string variable, even though that is more bothersome
to create.

It might be nice to have this in .cmod files automatically.