The matrix g  can have CV_32F or CV_64F type,  but g.at uses only float template.
This fix adds specialization for double type.

Revise some descriptions of the enums.

Merged android.toolchain.cmake from project
https://github.com/taka-no-me/android-cmake
commit: fd1f7055f8b7338644d58d9a2015a784dfa3a5ca

If we have perfect matches (min_dist == 0.0), then strict comparison
fails. Making it non-strict results in treating perfect matches as
good.

weights array is only allocated for (l_count+1) elements,
but then weights[l_count+1] element is accessed.

1. As getDevice will implicitly call setDevice, in getContext we should not need to call it again.
2. Fix an incorrect type casting.

It was merged by mistake.

This reverts commit ab6be9b7.

Test cases (accuracy and performance) are provided.