Pull

1. ~~choose candidate modifiers setting fixes. (for five addons)~~
2. ~~support both lua 5.1/5.2 (in c, by lilydjwg)~~
3. ~~use pkg-config to find lua (and option to specify version)~~
4. ~~workaround for bash bug.~~
5. [xkb] allow non-xmodmap with no arguement, only use ~/.Xmodmap for default command, free default script name
6. fix unicode prev/next page key (bug introduced in previous pull request T-T)
7. fix po targets related errors
8. fix extract-table-data dependencies
9. disable gettext support by option and when required libraries (libgettextpo.so) / executables (msgfmt) are not found. (This will also disable gettext support for all modules built with the same build tool (fcitx-po-parser).)