checkxalloc: nudge regex, fix newfound instances

checkxalloc: nudge regex, fix newfound instances

Using the -w flag with grep actually fought against us here, and hid
some instances where xalloc functions weren't used. Discard it in
favor of an explicit word boundary as a prefix to the function name,
and extend our requirements on the trailing side of the pattern.

This also fixes the few new instances that were overlooked because of
the regex's deficiency.

[kzak@redhat.com: - fix also newfound in findmnt
                  - remove unnecessary checks after xallocs]

Signed-off-by: Dave Reisner <dreisner@archlinux.org>
Signed-off-by: Karel Zak <kzak@redhat.com>