Deprecating oct_file_in_path and mex_file_in_path

[Rik]

3/8/16

All,

Unless someone can claim a use for them, I am going to deprecate
oct_file_in_path and mex_file_in_path.  These are located in
libinterp/corefcn/utils.cc.

They were added in 2006, but aren't used anywhere in the core, or in
Octave-Forge, that I can see.  The code itself is slightly incorrect, but
rather than fix it I would remove it entirely to minimize the number of
lines to maintain.

--Rik