Fixes consist in:
- no use of comma operator for multi statement purpose
- avoid confusing comma in for loops first and third clauses
- avoid implicit long to int casts by storing to long, or explicit bound checking before cast

Functions should only be prefixed with 'pj_' when they can be used in
other parts of the code base and not just within a single file.

Takes care of the last step in #675.

Closes #582

* Handle allocation failure when loading grid files

Continuing #606, we tackle the same issues in the loading and processing
of grid files. This should fix potential crashes and memory leaks, and
makes sure the global lock is always released.

* Use pj_calloc when zero-initialized memory is wanted

* Prevent crashes and leaks on allocation failure

Memory allocation can fail. We need to gracefully handle this case and
prevent dereferencing null pointers.

* Make NULL checks consistent within a file

* Properly report allocation errors

* Improve cleanup in pj_gc_reader.c

* Implement pj_strdup and use instead of strdup

The function strdup is not part of ANSI C 89, but a POSIX extension.
Therefore we can not rely on it being available on all platforms.

This is to address PR #341 in which Visual C++ stops compile due to encountering a #warning.

Remove setlocale() use in pj_init_ctx(), and replace uses of atof() &
strtod() by their locale safe variants pj_atof() and pj_strtod().
Proj versions from now advertize #define PJ_LOCALE_SAFE 1 in proj_api.h
and export pj_atof() & pj_strtod()