Merge commit 'osx-fixes' into unification/master

SDL on OS X does not include pkg-config files, so assume the user put it
in the OS X specific "framework" directory.

Reported by btb: https://github.com/dxx-rebirth/dxx-rebirth/issues/14
Requested by btb: https://github.com/dxx-rebirth/dxx-rebirth/issues/15
Search for SDL_mixer pkg-config too

Users might install SDL and SDL_mixer to separate paths, so search for
SDL_mixer.pc too.
use correct path for bundle executable
use correct path for localized strings
Simplify by using generic Info.plist, builtin substitions
<string> required for std::string
Merge pull request #16 from btb/osx-issues

Osx issues
Combine pkg-config caches
Fix escaping empty flags
Rewrite gr_linear_rep_movsdm with std::transform

Eliminate deprecated register.
Refactor gr_ubitmap012
Pack listbox better
Use range_for in light rendering
Rewrite scale_line to use std::fill

Eliminate inline byte-by-byte store.
Fix some -Wsign-compare warnings
Use pkg-config on Darwin if available
Extend in-game esc menu with options and saving
Fix crash on UDP initialization
Use array<> for team_kills
Fix loading robots-?.mvl

Rework movie loading to fix loading built-in robot movies.  The previous
code always ignored loading the last entry in the movie array, which was
blank until 18f6919b3308a33aa9d457a80772c274e5af456a.  The last entry
was unused after d38a3d136258526577717f820f9d1cf011f61cb6, so it was
removed, which caused the code to skip the robots entry.

Commit d38a3d136258526577717f820f9d1cf011f61cb6 broke unloading add-on
movies by removing the strcpy which saved their name.  Add code to save
the name to extra_robot_movie_mission and call it when switching
missions.

Reported by btb: https://github.com/dxx-rebirth/dxx-rebirth/pull/17