Fix search of parent directory in python script

Modify function `_PathsToAllParentFolders` to be compatible with
Windows filesystem.
Fix problem with function `_PathsToAllParentFolders` which does not
handle Windows system drive in the file path properly.
Merge branch 'python-parent-directory-search-fix' into develop
Improve the build system

Reduce configuration code copying between 'BoostParts' and 'ycm'
modules.
Now defenitions of 'BoostParts' are being cached.
Improve the build system

Reduce configuration code copying between 'BoostParts' and 'ycm'
modules.
Now cxx flags of 'BoostParts' module are being cached.
Merge branch 'mingw64-support' into develop