escaping password, to avoid it being interpretted as part of the command

I had trouble the first time I tried running sql-sync-pipe because some characters in the database password were being interpreted as part of the mysqldump command. I looked at how drush escapes passwords and adapted that for this patch. Based on drush's sql.drush.inc, probably all the pieces of the command should be escaped, but the small change included here solved my particular problem.

By the way, sql-sync-pipe decreased my import time from 27m7.149s to 15m16.875s. And that's after I'd already previously optimized the import by using --no-ordered-dump. Thanks!