Remove the hardcoded algorithm-type dependency for the SSLCertificateFile

Remove the hardcoded algorithm-type dependency for the SSLCertificateFile
and SSLCertificateKeyFile directives, and deprecate SSLCertificateChainFile

Splitting the patch into smaller pieces turned out to be infeasible,
unfortunately, due to the heavily intertwined code in ssl_engine_config.c,
ssl_engine_init.c and ssl_engine_pphrase.c, which all depends on the
modssl_pk_server_t data structure. For better comprehensibility,
a detailed listing of the changes follows:

ssl_private.h
- drop the X509 certs and EVP_PKEY keys arrays from modssl_pk_server_t
- use apr_array_header_t for cert_files and key_files
- drop tPublicCert from SSLModConfigRec
- drop the ssl_algo_t struct and the SSL_ALGO_* and SSL_AIDX_* constants

ssl_engine_config.c
- change to apr_array_header_t for SSLCertificate[Key]File
- drop ssl_cmd_check_aidx_max, i.e. allow an arbitrary number of certs
  and keys (in theory; currently OpenSSL does not support more than
  one cert/key per algorithm type)
- add deprecation warning for SSLCertificateChainFile

ssl_engine_init.c
- configure server certs/keys in ssl_init_server_certs (no longer via
  ssl_pphrase_Handle in ssl_init_Module)
- in ssl_init_server_certs, read in certificates and keys with standard
  OpenSSL API functions (SSL_CTX_use_*_file), and only fall back to
  ssl_load_encrypted_pkey when encountering an encrypted private key
- drop ssl_server_import_cert, ssl_server_import_key, ssl_init_server_check,
  and ssl_init_ctx_cleanup_server
- move the "problematic re-initialization" check to ssl_init_server_ctx

ssl_engine_pphrase.c
- use servername:port:index as the key identifier, instead of the
  previously used servername:port:algorithm
- ssl_pphrase_Handle overhaul: remove all cert/public-key handling,
  make it only load a single (encrypted) private key, and rename
  to ssl_load_encrypted_pkey
- in the passphrase prompt message, show the private key file name
  instead of the vhost id and the algorithm name
- do no longer supply the algorithm name as an argument to "exec"-type
  passphrase prompting programs

ssl_util.c
- drop ssl_util_algotypeof, ssl_util_algotypestr, ssl_asn1_keystr,
  and ssl_asn1_table_keyfmt

ssl_util_ssl.{c,h}
- drop SSL_read_X509
- constify the filename arg for SSL_read_PrivateKey

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1553824 13f79535-47bb-0310-9956-ffa450edef68