Minor modifications.

    * regex.jam (split): Change behavour with regard to separators at
	the beginning of string.
    * os.path.jam (has_parent, parent, join): Allow relative paths to
	point upward.
	(all_parents): new rule
	Added support for unix pathes.


[SVN r13279]

tools/build

@@ -1 +1 @@
-Subproject commit 18c3412b841b6dbd5c690c2df7c19fd2bc47f783
+Subproject commit 6804ee73737b77659510c6fba83192833d34fa33