do not update binaries when Cancel is pressed

in the tkFileDialog, if cancel is pressed, dssp_bin and stride_bin is not updated now (they were set to empty strings in old version).
do not update binaries or directories when Cancel

in FileDialog if cancel is pressed do not update corresponding variables.
add comments (test)
do not update binaries when Cancel is pressed

in the tkFileDialog, if cancel is pressed, dssp_bin and stride_bin is not updated now (they were set to empty strings in old version).
do not update binaries or directories when Cancel

in FileDialog if cancel is pressed do not update corresponding variables.
add comments (test)
Merge branch 'master' of https://github.com/hongbo-zhu-cn/Pymol-script-repo

Conflicts:
	plugins/msms.py
Merge pull request #48 from hongbo-zhu-cn/master

do not update binaries when Cancel is pressed