STYLE: Remove references to std:: inside KWSys, even in comments.  This will allow a commit check to be added.

BUG: Make sure search paths never have double-slashes.  Leading with two slashes (//) on cygwin looks like a network path and delays while waiting for a non-existent machine.

ENH: Improved escaping in kwsys/System.  Added escape of % for NMake.  Added escape of ; for the VS IDE.

ENH: Add SystemTools::SplitPathRootComponent and re-implement SplitPath to use it.  Add better treatment of user home directory paths.

BUG: Fix hang in Process_Kill on OS X caused by an OS bug in which a pipe read end cannot be closed if the pipe write end is open, the pipe is full, and another process is blocking waiting to write.  Work around the problem by killing the children before closing the pipes.