pgcrypto: report init errors as PXE_CIPHER_INIT

Report OpenSSL errors during initialization as PXE_CIPHER_INIT since
that's just what they were, and not generic unknown errors. This also
removes the last users of the generic error, and thus it can be removed.

Discussion: http://postgr.es/m/C89D932C-501E-4473-9750-638CFCD9095E@yesql.se

contrib/pgcrypto/openssl.c

@@ -209,13 +209,13 @@ px_find_digest(const char *name, PX_MD **res)
 	if (!ctx)
 	{
 		pfree(digest);
-		return -1;
+		return PXE_CIPHER_INIT;
 	}
 	if (EVP_DigestInit_ex(ctx, md, NULL) == 0)
 	{
 		EVP_MD_CTX_destroy(ctx);
 		pfree(digest);
-		return -1;
+		return PXE_CIPHER_INIT;
 	}
 
 	digest->algo = md;

contrib/pgcrypto/px.c

@@ -41,7 +41,6 @@ struct error_desc
 
 static const struct error_desc px_err_list[] = {
 	{PXE_OK, "Everything ok"},
-	{PXE_ERR_GENERIC, "Some PX error (not specified)"},
 	{PXE_NO_HASH, "No such hash algorithm"},
 	{PXE_NO_CIPHER, "No such cipher algorithm"},
 	{PXE_BAD_OPTION, "Unknown option"},

contrib/pgcrypto/px.h

@@ -44,7 +44,7 @@
  * PX error codes
  */
 #define PXE_OK						0
-#define PXE_ERR_GENERIC				-1
+/* -1 is unused */
 #define PXE_NO_HASH					-2
 #define PXE_NO_CIPHER				-3
 /* -4 is unused */