Parsing of PKCS#8 encrypted private key files added and PKCS#12 basis

PKCS#8 encrypted key file support has been added to x509parse_key() with
support for some PCKS#12 PBE functions (pbeWithSHAAnd128BitRC4,
pbeWithSHAAnd3-KeyTripleDES-CBC and pbeWithSHAAnd2-KeyTripleDES-CBC)
diff --git a/include/polarssl/error.h b/include/polarssl/error.h
index 73ebe89..1f7469c 100644
--- a/include/polarssl/error.h
+++ b/include/polarssl/error.h
@@ -74,6 +74,7 @@
  * High-level module nr (3 bits - 0x1...-0x8...)
  * Name     ID  Nr of Errors
  * PEM      1   9
+ * PKCS#12  1   3 (Started from top)
  * X509     2   21
  * DHM      3   6
  * RSA      4   9