devfs: optionally add missing symbolic links

If symbolic links for /dev/{fd,stdin,stdout,stderr,core} do not exist
once /dev is mounted, we should create them.
init.d: add osclock to ignore patterns
Fix mdoc warning for empty line in rc-update man page.

X-Gentoo-Bug: 529374
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=529374
Make sysfs behave like netmount and localmount

sysfs now mounts all related sysfs file systems and returns success,
like netmount and localmount.

Also, we now check to make sure the cgroups are not mounted before we
mount them.

X-Gentoo-Bug: 530138
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=530138
rename git.mk to gitver.mk

This is a more descriptive name since this file only sets the gitver
variable.