Minor grammar improvements to documentation
Assorted fixes:

* cmake CMP0054 and CMP0045
* aarch64 build
* portable code options in PCH cmake
* some of gcc 4.9 warnings
Fix Android build with the most resent android.toolchain.cmake
fix tests for gpu::matchTemplate:

use ASSERT_FLOAT_EQ to compare float values, it is more robust for
large values
Merge pull request #3545 from jet47:gpu-match-template-tests
Merge pull request #3543 from MatMoore:2.4
Merge pull request #3534 from taka-no-me:build_fixes