Start refactoring of htpasswd and htdbm

- Move many common code parts into separate source file. This adds some
  of htpasswd's recent improvements to htdbm.
- Rework salt generation to use the full 48bit of entropy for MD5
  Previously, it would only generate 2^32 different salts on a given
  platform.
- Use apr_getopt().


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1395253 13f79535-47bb-0310-9956-ffa450edef68