build: search from newest to oldest for gmime.

We (Gentoo distribution) reckon that in the case of multiple versions of
gmime installed we should prefer the newest one.

Change-Id: Idf7be613230232eb1d573d93c4a5a8297f4ecd2d

configure

@@ -31796,7 +31796,7 @@ fi
     fi
 fi
 
-for ver in 2.0 2.2 2.4 2.6 3.0; do
+for ver in 3.0 2.6 2.4 2.2 2.0; do
 
    if test "x${PBX_GMIME}" != "x1" -a "${USE_GMIME}" != "no"; then
 

configure.ac

@@ -2660,7 +2660,7 @@ then
     fi
 fi
 
-for ver in 2.0 2.2 2.4 2.6 3.0; do
+for ver in 3.0 2.6 2.4 2.2 2.0; do
 	AST_PKG_CONFIG_CHECK([GMIME], gmime-$ver)
 	if test "$PBX_GMIME" = 1; then
 		break;