new formula: xplanetFX 2.5.24

xplanetFX is a program that manipulates Xplanet renderings with lighting effects using ImageMagick.
Fixing Caveat Text
Removing gnu-sed default name option

by replacing all occurrences of "sed" in script to "gsed"
Commit addressing all discussed issues...

1. Using EOS in the caveat section
2. Using gsed instead of sed
3. Using "if build.with?" instead of "unless build.without?"
4. Confirming X11 is a required dependent
reflecting change in pygtk formula
Updating to xplanetFX 2.5.25...

which checks for gsed.  Also removed the " sed" to " gsed" inreplace as  aresult.
removing gnu-sed path addition in caveats
forcing python dependency and added wrapper script

Dealing with the vagaries related to python - not depending on it and having to set PYTHONPATH or trying to `depends_on :python` proved too complicated.  Adding the wrapper script to set the other two env. variables, PERL5LIB and GDK_PIXBUF_MODULEDIR cleaned up the caveats section.
deleting trailing whitespace
removed Homebrew python dependency
xplanetfx: add 2.5.25 bottle.