fix wrong paths showing up in pkg-config files

-the wrong libdir path was written if a full path is passed to scons instead of
 one relative to "prefix", i.e. "/usr/lib64" instead of "lib64"
-the includedir passed to scons was entirely ignored

Qgpsmm.pc.in

@@ -1,7 +1,7 @@
 prefix=@prefix@
 exec_prefix=${prefix}
-libdir=${exec_prefix}@libdir@
-includedir=${prefix}/include
+libdir=@libdir@
+includedir=@includedir@
 qt_config=lex yacc warn_on uic resources qt release incremental link_prl def_files_disabled exceptions no_mocdepend stl qt_no_framework create_pc create_prl moc thread dll
 
 Name: Qgpsmm

SConstruct

@@ -1509,7 +1509,8 @@ def substituter(target, source, env):
     substmap = (
         ('@VERSION@',    gpsd_version),
         ('@prefix@',     env['prefix']),
-        ('@libdir@',     env['libdir']),
+        ('@libdir@',     installdir('libdir', add_destdir=False)),
+        ('@includedir@',     installdir('includedir', add_destdir=False)),
         ('@udevcommand@',    udevcommand),
         ('@DATE@',       time.asctime()),
         ('@MASTER@',     'DO NOT HAND_HACK! THIS FILE IS GENERATED'),

libgps.pc.in

@@ -1,7 +1,7 @@
 prefix=@prefix@
 exec_prefix=${prefix}
-libdir=${exec_prefix}/@libdir@
-includedir=${prefix}/include
+libdir=@libdir@
+includedir=@includedir@
 
 Name: GPSD
 Description: GPS Daemon communication library