Move away from openvpn_basename() over to platform provided basename()

Move away from openvpn_basename() over to platform provided basename()

This kicks out the openvpn_basename() function from misc.[ch] and puts
glibc equivalents into compat.[ch].  This is to provide the same
functionality on platforms not having a native basename() function
available.

In addition this patch adds dirname() which commit 0f2bc0dd92f43c91e
depends.  Without dirname(), openvpn won't build in Visual Studio.

v2: Move all functions from compat.h to compat.c
v3: Use glibc versions of basename() and dirname() instead

Signed-off-by: David Sommerseth <davids@redhat.com>
Acked-by: Alon Bar-Lev <alon.barlev@gmail.com>
URL: http://thread.gmane.org/gmane.network.openvpn.devel/5178/focus=5215