add openssl signing support. This adds an extra parameter

add openssl signing support.  This adds an extra parameter
for the contents of the exported private key to Phar->setSignatureAlgorithm, and expects the public key to be in
a file named blah.phar.pubkey in the same directory as the phar blah.phar.  This works with openssl static or
shared and fails gracefully if openssl is not present without adding a dependency. config.w32 needs updating to match config.m4 [DOC]