Internally split up x509parse_key()

Split up x509parse_key() into a (PEM) handler function and specific
DER parser functions for the PKCS#1 (x509parse_key_pkcs1_der()) and
unencrypted PKCS#8 (x509parse_key_pkcs8_unencrypted_der()) private
key formats.
diff --git a/ChangeLog b/ChangeLog
index 7561aba..0a4bfb1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,6 +3,9 @@
 = Branch 1.2
 Change
    * HAVEGE random generator disabled by default
+   * Internally split up x509parse_key() into a (PEM) handler function
+     and specific DER parser functions for the PKCS#1 and unencrypted
+     PKCS#8 private key formats
 
 Bugfix
    * Secure renegotiation extension should only be sent in case client