Added and improved READMEs for modules whihc used to be in libs-extern

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+XML signing, etc. From [http://www.aleksey.com/xmlsec/]. Heavily patched.
+
+The XML Security library has been modified, so that there is NO verification of
+the certificate during sign or verification operation. On Windows this was done
+in the function xmlSecMSCryptoX509StoreVerify (file src/mscrypto/x509vfy.c) and
+on UNIX in xmlSecNssX509StoreVerify (file src/nss/x509vfy.c).
+
+The implementation creates certificates from all of the X509Data children, such
+as X509IssuerSerial and X509Certificate and stores them in a certificate store
+(see xmlsec/src/mscrypto/x509.c:xmlSecMSCryptoX509DataNodeRead). It must then
+find the certificate containing the public key which is used for validation
+within that store. This is done in xmlSecMSCryptoX509StoreVerify. This function
+however only takes those certificates into account which can be validated. This
+was changed by the patch xmlsec1-noverify.patch, which prevents this certificate
+validation.
+
+xmlSecMSCryptoX509StoreVerify iterates over all certificates contained or
+referenced in the X509Data elements and selects one which is no issuer of any of
+the other certificates. This certificate is not necessarily the one which was
+used for signing but it must contain the proper validation key, which is
+sufficient to validate the signature. See 
+http://www.w3.org/TR/xmldsig-core/#sec-X509Data 
+for details.
+
+There is a flag XMLSEC_KEYINFO_FLAGS_X509DATA_DONT_VERIFY_CERTS that can be set
+in a xmlSecKeyInfoCtx (see function xmlSecNssKeyDataX509XmlRead, in file
+src/nss/x509.c), which indicates that one can turn off the validation. However,
+setting it will cause that the validation key is not found. If the flag is set,
+then the key is not extracted from the certificate store which contains all the
+certificates of the X509Data elements. In other words, the certificates which
+are delivered within the XML signature are not used when looking for suitable
+validation key.
+
+