Add support for SHA-2 crypt() algorithm in htpasswd.

Add support for SHA-2 crypt() algorithm in htpasswd.

* configure.in: Detect SHA-2 support in crypt().

* support/passwd_common.h: Define ALG_CRYPT_SHA256, ALG_CRYPT_SHA512,
  include ap_config_auto.h.

* support/htpasswd.c (check_args): Allow -2, -5, -r arguments for
  SHA-256, SHA-256 and rounds options respectively.

* support/passwd_common.c
  (parse_common_options): Parse -2, -5, -r args.
  (mkhash): Generate crypt hash for SHA256/SHA512 algorithms.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1861793 13f79535-47bb-0310-9956-ffa450edef68