Disabled BORDER_CONSTANT for pyramid functions.
export BOW to script wrappers
add Bag of Words to python wrapper
Fix typos
Updated findHomography docs branch 2.4

Updated the documents to give warning to the users of `findHomography` that the function may return an empty matrix in some cases. 
The user must take care of checking that.
Merge pull request #2843 from berak:f_export_bow_24
Merge pull request #2868 from neo008:2.4
Merge pull request #2870 from 23pointsNorth:patch-5
Fixing build error when using post-increment operator.
Fixed android and windows x64 build issues
Fix for Bug#3757: All dimension values are 0 after release is called
Merge pull request #2889 from Ilya-Krylov:fisheye
Merge pull request #2891 from nisargthakkar:dims_zero_on_release
Merge pull request #2880 from GravityJack:SparseMatIterator-build-fix
Merge pull request #2766 from akarsakov:pyr_border_constant
Merge remote-tracking branch 'origin/2.4' into issue3258