scripts: better sanitise the patch names

When generating the fixes-patches, better sanitise the generated
file names, as it seems to raise a few issues for some people.

scripts/mk-patch.sh

@@ -34,7 +34,7 @@ hg -R "${repos}" log -b "${branch}" -r "${r1}:tip" --template '{rev}\n'    \
         continue
     fi
     plog=$( hg -R "${repos}" log -r ${rev} --template '{desc|firstline}\n'  \
-            |sed -r -e 's,[/ :]+,_,g;'                                      \
+            |sed -r -e 's,[/:,[:space:]],_,g; s/_+/_/g;'                    \
           )
     pname="${p}-${plog}.patch"
     printf "Revision '%d' --> '%s'\n" ${rev} "${pname}"