Refactor inc_release script to allow reusing parts of it

No real changes, just extract the useful helpers from this script into
another file.

misc/scripts/inc_release

@@ -8,52 +8,7 @@
 # Licence:    wxWindows licence
 ##############################################################################
 
-error() {
-    echo "$progname: $*" >&2
-}
-
-msg() {
-    echo "$progname: $*"
-}
-
-msgn() {
-    echo -n "$progname: $*"
-}
-
-msgc() {
-    echo "$*"
-}
-
-run_sed() {
-    filename=$1
-    shift
-    cmd=
-    while [ $# -gt 0 ]; do
-        cmd="$cmd-e \"$1\" "
-        shift
-    done
-
-    msgn "	processing $filename ...	"
-    eval "sed $cmd $filename" > $filename.$$
-    if cmp -s $filename $filename.$$; then
-        rm $filename.$$
-        msgc "unchanged"
-    else
-        mv $filename.$$ $filename
-        msgc "done"
-    fi
-}
-
-progname=`basename $0`
-
-# we must be run from wx directory
-if [ ! -f wxwin.m4 ]; then
-    error "must be ran from root wx directory"
-    exit 1
-fi
-
-# exit on any error
-set -e
+. `dirname $0`/run_sed_common.sh
 
 # the primary source of information is wx/version.h
 ver_string=`grep '#define wxVERSION_STRING ' include/wx/version.h | sed 's/^.*"wxWidgets \(.*\)")/\1/'`