x11/libXext: Update to 1.3.4

Update x11/libXext to 1.3.4.
This release contains misc bugfixes, typo fixes and build system
updates.

pet portlint by moving USES and CPE information earlier.
add LICENSE_FILE

Changelog:
https://lists.x.org/archives/xorg-announce/2019-March/002975.html

Sponsored by: B3 Init