warn and continue gracefully if bcmath is not installed
make tests deal with missing bcmath
Pass existing Net_SFTP object into Net_SFTP_Stream.
Merge pull request #9576 from owncloud/bcmath-check

LDAP Active Directory Primary Groups support depends on bcmath module
Merge pull request #9720 from owncloud/sftp-stream-wrapper-new-connection

Pass existing Net_SFTP object into Net_SFTP_Stream.