dev-libs/sway: various fixes

dev-libs/sway: various fixes

 - Use ${PN} wherever possible;

 - Remove bash-completion use flag: bash completions should be always
   installed (see [1]);

 - Remove clipboard use flag and related dep: makes no sense to add this
   here, if the user wants to add utilities to handle the clipboard under
   wayland it is just and emerge away; wl-clipboard has nothing to do
   with sway;

 - Rename use flag: doc -> man (doc is a global use flag used to install
   additional documentation that most users does not want);

 - The sway tray feature (enabled by the tray use flag) now requires a
   logind provider: reflect this in REQUIRED_USE (fixes #677748);

 - Fix order of (R)DEPEND;

 - Remove required use gdk-pixbuf[jpeg]: the jpeg use flag is not
   required to be enabled. If the user wants support for JPEG images, he
   can manually enable it in gdk-pixbuf (as for other img formats);

 - Remove libcap dep: the fcaps eclass automatically adds it if filecaps
   use flag is enabled;

 - Dependency dbus is no longer required with tray (now uses sd-bus from
   logind): remove anything related to it;

 - Move scdoc and wayland-protocols dependencies to BDEPEND;

 - Add dep on xkeyboard-config: see bug #674640;

 - Add man-pages parameter to meson (fixes bug #677654);

 - Disable swaybar man page installation when swaybar use flag is
   disabled;

 - Use $MY_PV in sway-version arg to meson to reflect upstream version
   in sway --version;

 - Add a reminder to set XDG_RUNTIME_DIR if it's not set by the
   environment. This is needed in systems without logind/consolekit.

[1] www.gentoo.org/support/news-items/2014-11-25-bash-completion-2_1-r90.html

Closes: https://bugs.gentoo.org/672590
Closes: https://bugs.gentoo.org/675978
Closes: https://bugs.gentoo.org/674640
Closes: https://bugs.gentoo.org/677654
Closes: https://bugs.gentoo.org/677748
Package-Manager: Portage-2.3.59, Repoman-2.3.12
Signed-off-by: Niccolò Scatena <speedjack95@gmail.com>
Signed-off-by: Aaron Bauman <bman@gentoo.org>