Clean house in cryptographic hashing code

Clean house in cryptographic hashing code

- Remove dead code from php_crypt_r.c

  This code has been commented out since the file was added in 2008. It's safe to say
  that no-one is ever going to use it.

- Fix typo in comment in php_crypt_r.c

- Remove redundant Windows-only implementation of php_md5_crypt_r

  There is a portable implementation in the same file, which is selected if not
  building for Windows. But why should Windows have its own special implementation
  of this function at all? There doesn't seem to be any good reason.

  Better to use the portable implementation on all platforms.

- Don't define useless __CONST macro in php_crypt_r.h

  This preprocessor macro is not used anywhere.

- Add comment on functions for encoding data as Base64

- Remove dead code from crypt_blowfish.h

- Remove unneeded junk comments from crypt_freesec.c

- Remove dead code from crypt_blowfish.c

  This function has been commented out since 2011.