Windows treats '\\' and '/' equivalently but we cannot control
the form that will be used by end users. Introduce ISPATHSEP()
macro which tests only for '/' on UNIX and both on Windows.
Introduce ISTILDE() macro to test for '~'. When testing for
'/' with strchr() or strrchr() add conditional checks for '\\' on
Windows.
Change-Id: Ia85e698fc88f15a6a71db649db5417f02ef7e5fe