Add comment to make code for option-stripping in mysql_config more clear

scripts/mysql_config.sh:
  Add comment to clarify why we can safely only strip flags with a leading space

scripts/mysql_config.sh

@@ -100,6 +100,8 @@ for remove in DDBUG_OFF DSAFEMALLOC USAFEMALLOC DSAFE_MUTEX \
               DPEDANTIC_SAFEMALLOC DUNIV_MUST_NOT_INLINE DFORCE_INIT_OF_VARS \
               DEXTRA_DEBUG DHAVE_purify 'O[0-9]' 'W[-A-Za-z]*'
 do
+  # The first option we might strip will always have a space before it because
+  # we set -I$pkgincludedir as the first option
   cflags=`echo "$cflags"|sed -e "s/ -$remove  */ /g"` 
 done
 cflags=`echo "$cflags"|sed -e 's/ *\$//'`