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)
(cherry picked from commit cf6e95d9a81c7b22271beb58a09b5c756148e62a)

Conflicts:
	scripts/generate_errors.pl
diff --git a/include/polarssl/error.h b/include/polarssl/error.h
index cb8840c..9a3de00 100644
--- a/include/polarssl/error.h
+++ b/include/polarssl/error.h
@@ -76,6 +76,7 @@
  * 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