various save_*() calls for saving images.

are saved to disk by the various save_*() functions.

the target pixel was an RGB pixel with an alpha channel.

to dlib::hash().

--HG--
rename : dlib/test/bridge.cpp => dlib/test/hash.cpp

additional convenience functions.

if a type can be swapped rather than the explicit union trick.

This way I can change just this one macro to use the better C++0x
method of doing this check once C++0x becomes available.

syntax but to use the array2d<type> syntax.

anymore to declare it.  Now you just say array2d<type>.

then calls the appropriate image loading function.