core: install weechat.desktop with autotools (issue #982, issue #408)

Makefile.am

@@ -66,6 +66,7 @@ EXTRA_DIST = AUTHORS.adoc \
              tools/git-version.sh \
              tools/makedist.sh \
              version.sh \
+             weechat.desktop \
              weechat.png \
              weechat.pc.in \
              weechat.cygport.in
@@ -78,5 +79,8 @@ pkgconfig_DATA = weechat.pc
 icondir = $(datadir)/icons/hicolor/32x32/apps
 icon_DATA = weechat.png
 
+desktopdir = $(datadir)/applications
+desktop_DATA = weechat.desktop
+
 clean-local:
 	$(RM) config-git.h