library: Fix pkglibdir of backends

autoreconf errored out with:
src/lib/datasrc/Makefile.am:34: `pkglibexecdir' is not a legitimate directory for `LTLIBRARIES'

and consecutive errors such as:
src/lib/datasrc/Makefile.am:43: variable `memory_ds_la_SOURCES' is defined but no program or
src/lib/datasrc/Makefile.am:43: library has `memory_ds_la' as canonical name (possible typo)
src/lib/datasrc/Makefile.am:36: variable `sqlite3_ds_la_SOURCES' is defined but no program or
src/lib/datasrc/Makefile.am:36: library has `sqlite3_ds_la' as canonical name (possible typo)
src/lib/datasrc/Makefile.am:45: variable `memory_ds_la_LIBADD' is defined but no program or
src/lib/datasrc/Makefile.am:45: library has `memory_ds_la' as canonical name (possible typo)
src/lib/datasrc/Makefile.am:39: variable `sqlite3_ds_la_LIBADD' is defined but no program or
src/lib/datasrc/Makefile.am:39: library has `sqlite3_ds_la' as canonical name (possible typo)
src/lib/datasrc/Makefile.am:44: variable `memory_ds_la_LDFLAGS' is defined but no program or
src/lib/datasrc/Makefile.am:44: library has `memory_ds_la' as canonical name (possible typo)
src/lib/datasrc/Makefile.am:37: variable `sqlite3_ds_la_LDFLAGS' is defined but no program or
src/lib/datasrc/Makefile.am:37: library has `sqlite3_ds_la' as canonical name (possible typo)

According to automake "bug#7647: Diagnose invalid primary/directory combinations"
as in http://www.mail-archive.com/bug-automake@gnu.org/msg01927.html

we nowadays have to use pkglibdir for LTLIBRARIES, not pkglibexecdir.

+2010-12-17  Stefano Lattarini  <stefano.lattar...@gmail.com>
+
+	Warnings about primary/prefix mismatch fixed and extended.
+	* automake.in (%standard_prefix): Add `doc' and `locale'.
+	Rename `pkgdatadir' to `pkgdata'.  Similarly for`pkglibdir',
+	`pkgincludedir' and `pkglibexecdir'.
+	(handle_programs): List `pkglibexec', not `pkglib', among the
+	prefixes valid for the `PROGRAMS' primary.
[]
+for primary in $primaries; do
+  prefixes_ok=''
+  case $primary in
+    LIBRARIES|LTLIBRARIES)
+      prefixes_ok='lib pkglib'
+      ;;
+    PROGRAMS)
+      prefixes_ok='bin sbin libexec pkglibexec'
+      ;;

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

src/lib/datasrc/Makefile.am

@@ -7,10 +7,10 @@ AM_CPPFLAGS += $(SQLITE_CFLAGS)
 
 AM_CXXFLAGS = $(B10_CXXFLAGS)
 
-pkglibexecdir = $(libexecdir)/@PACKAGE@/backends
+pkglibdir = $(libexecdir)/@PACKAGE@/backends
 
 datasrc_config.h: datasrc_config.h.pre
-	$(SED) -e "s|@@PKGLIBEXECDIR@@|$(pkglibexecdir)|" datasrc_config.h.pre >$@
+	$(SED) -e "s|@@PKGLIBDIR@@|$(pkglibdir)|" datasrc_config.h.pre >$@
 
 CLEANFILES = *.gcno *.gcda datasrc_messages.h datasrc_messages.cc
 CLEANFILES += datasrc_config.h
@@ -31,7 +31,7 @@ libdatasrc_la_SOURCES += database.h database.cc
 libdatasrc_la_SOURCES += factory.h factory.cc
 nodist_libdatasrc_la_SOURCES = datasrc_messages.h datasrc_messages.cc
 
-pkglibexec_LTLIBRARIES =  sqlite3_ds.la memory_ds.la
+pkglib_LTLIBRARIES =  sqlite3_ds.la memory_ds.la
 
 sqlite3_ds_la_SOURCES = sqlite3_accessor.h sqlite3_accessor.cc
 sqlite3_ds_la_LDFLAGS = -module