Misc m4 cleanups

Whitespace cleanups
Use m4_default instead of some ifelses.

Thanks to Stepan Kasal for the patch this is based on
Bug #13892

pkg.m4

@@ -43,7 +43,6 @@ if test -n "$PKG_CONFIG"; then
 		AC_MSG_RESULT([no])
 		PKG_CONFIG=""
 	fi
-		
 fi[]dnl
 ])# PKG_PROG_PKG_CONFIG
 
@@ -61,12 +60,11 @@ AC_DEFUN([PKG_CHECK_EXISTS],
 [AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
 if test -n "$PKG_CONFIG" && \
     AC_RUN_LOG([$PKG_CONFIG --exists --print-errors "$1"]); then
-  m4_ifval([$2], [$2], [:])
+  m4_default([$2], [:])
 m4_ifvaln([$3], [else
   $3])dnl
 fi])
 
-
 # _PKG_CONFIG([VARIABLE], [COMMAND], [MODULES])
 # ---------------------------------------------
 m4_define([_PKG_CONFIG],
@@ -129,7 +127,7 @@ if test $pkg_failed = yes; then
 	# Put the nasty error message in config.log where it belongs
 	echo "$$1[]_PKG_ERRORS" >&AS_MESSAGE_LOG_FD
 
-	ifelse([$4], , [AC_MSG_ERROR(dnl
+	m4_default([$4], [AC_MSG_ERROR(
 [Package requirements ($2) were not met:
 
 $$1_PKG_ERRORS
@@ -137,24 +135,23 @@ $$1_PKG_ERRORS
 Consider adjusting the PKG_CONFIG_PATH environment variable if you
 installed software in a non-standard prefix.
 
-_PKG_TEXT
-])],
-                [$4])
+_PKG_TEXT])dnl
+        ])
 elif test $pkg_failed = untried; then
      	AC_MSG_RESULT([no])
-	ifelse([$4], , [AC_MSG_FAILURE(dnl
+	m4_default([$4], [AC_MSG_FAILURE(
 [The pkg-config script could not be found or is too old.  Make sure it
 is in your PATH or set the PKG_CONFIG environment variable to the full
 path to pkg-config.
 
 _PKG_TEXT
 
-To get pkg-config, see <http://pkg-config.freedesktop.org/>.])],
-                [$4])
+To get pkg-config, see <http://pkg-config.freedesktop.org/>.])dnl
+        ])
 else
 	$1[]_CFLAGS=$pkg_cv_[]$1[]_CFLAGS
 	$1[]_LIBS=$pkg_cv_[]$1[]_LIBS
         AC_MSG_RESULT([yes])
-	ifelse([$3], , :, [$3])
+	$3
 fi[]dnl
 ])# PKG_CHECK_MODULES