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

OPENCLAMDBLAS and OPENCLAMDFFT never detected under linux.
lib64/import and lib32/import is the path on Windows but not Linux.
for CLAMDBLAS library we should use CLAMDBLAS_PATH (not CLAMDFFT_PATH)

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.