pkg-config: Relative paths

Define our completion and helper dirs using the standard data and sysconf
dirs. Enables 3rd party package staged installs by overriding these two
dirs, in addition to the already existing mechanisms.

Makefile.am

@@ -3,6 +3,7 @@ SUBDIRS = completions doc helpers test
 pkgdata_DATA = bash_completion
 
 # Empty, but here just to get the compat dir created with install
+compatdir = $(sysconfdir)/bash_completion.d
 compat_DATA =
 
 profiledir = $(sysconfdir)/profile.d
@@ -18,8 +19,9 @@ cmakeconfig_DATA = bash-completion-config.cmake \
 %: %.in Makefile
 	$(SED) \
 		-e 's|@prefix[@]|$(prefix)|' \
-		-e 's|@compatdir[@]|$(compatdir)|' \
-		-e 's|@pkgdatadir[@]|$(pkgdatadir)|' \
+		-e 's|@datadir[@]|$(datadir)|' \
+		-e 's|@sysconfdir[@]|$(sysconfdir)|' \
+		-e 's|@PACKAGE[@]|$(PACKAGE)|' \
 		-e 's|@VERSION[@]|$(VERSION)|' \
 		<$(srcdir)/$@.in >$@
 

bash-completion-config.cmake.in

@@ -4,8 +4,9 @@
 set (BASH_COMPLETION_VERSION "@VERSION@")
 
 set (BASH_COMPLETION_PREFIX "@prefix@")
-set (BASH_COMPLETION_COMPATDIR "@compatdir@")
-set (BASH_COMPLETION_COMPLETIONSDIR "@pkgdatadir@/completions")
-set (BASH_COMPLETION_HELPERSDIR "@pkgdatadir@/helpers")
+
+set (BASH_COMPLETION_COMPATDIR "@sysconfdir@/bash_completion.d")
+set (BASH_COMPLETION_COMPLETIONSDIR "@datadir@/@PACKAGE@/completions")
+set (BASH_COMPLETION_HELPERSDIR "@datadir@/@PACKAGE@/helpers")
 
 set (BASH_COMPLETION_FOUND "TRUE")

bash-completion.pc.in

@@ -1,7 +1,10 @@
 prefix=@prefix@
-compatdir=@compatdir@
-completionsdir=@pkgdatadir@/completions
-helpersdir=@pkgdatadir@/helpers
+datadir=@datadir@
+sysconfdir=@sysconfdir@
+
+compatdir=${sysconfdir}/bash_completion.d
+completionsdir=${datadir}/@PACKAGE@/completions
+helpersdir=${datadir}/@PACKAGE@/helpers
 
 Name: @PACKAGE@
 Description: programmable completion for the bash shell

configure.ac

@@ -8,7 +8,6 @@ AC_ARG_WITH([pytest],[  --with-pytest=executable],[PYTEST="$withval"])
 if test -z "$PYTEST"; then
     AC_CHECK_PROGS([PYTEST],[pytest pytest-3],[pytest])
 fi
-AC_SUBST(compatdir, $sysconfdir/bash_completion.d)
 AC_CONFIG_FILES([
 Makefile
 completions/Makefile