[m-rev.] Refactoring make_temp

[Paul Bone]

I've been refactoring make_temp.  My goal is to make this code more
consistent between the Mercury backends by implementing most of it in
Mercury and only calling out to the foreign code for the system calls.  My
work in progress is here:

    https://github.com/PaulBone/mercury/tree/make_temp

I've removed the weird 5-character limit to the filename's prefix.  Suffixes
work properly in C grades (probably the bug the Julien experienced).

I have the C and Java backends working, Java doesn't set the file modes
correctly, as that requires Java 1.7.  C# is partially implemented, I'd like
Sebastian's help to finish it.  And Erlang is not done at all.

I may fix the Erlang code later, but for now I need to go back to other
tasks.

Cheers.


-- 
Paul Bone