That allows BFile to actually create files (it didn't use that syscall at
all before).
Also fixed setting the permission bits of the newly created file depending on umask
(the __gUmask variable should probably be moved into a separate header).
git-svn-id: file:///srv/svn/repos/haiku/trunk/current@11208 a95241bf-73f2-0310-859d-f6bbb57e9c96