adding cap_images.cpp to android build, may fix link error, but not really address issue of reading video files on android

*fixed some warnings
*finished gpu test port to gtest framework

replaced alloca() (a.k.a. cvStackAlloc) with AutoBuffer or vector() everywhere. cvStackAlloc() is still defined, but we do not need alloca() anymore to compile and run OpenCV (fixes #889 and may be some others)

replaced alloca() (a.k.a. cvStackAlloc) with AutoBuffer or vector() everywhere. cvStackAlloc() is still defined, but we do not need alloca() anymore to compile and run OpenCV (fixes #889 and may be some others)

replaced alloca() (a.k.a. cvStackAlloc) with AutoBuffer or vector() everywhere. cvStackAlloc() is still defined, but we do not need alloca() anymore to compile and run OpenCV (fixes #889 and may be some others)

removed CMakeLists.txt from gpu/test folder to avoid precompiled header associated warnings under Ubuntu

fixed incorrect device id in multi_gpu sample (checked both multi GPU samples work correctly with new multi GPU API)

removed catch from GPU stereo_bp test as --gtest_catch_exceptions flags exists (but err msg isn't printed in case when there is no GPU)

Prefixed constants in flann with FLANN_ to prevent clashes with constants from other includes, closes bug #890

minor fixes and refactoring of GPU module

GPU: TargetArchs -> added FEATURE_SET prefix.