Bug 4631: security_file_certgen helper without disk cache (#95)

Bug 4631: security_file_certgen helper without disk cache (#95)

* disable the certificate DB disk cache if -s and -M command line options are omitted.

E.g. with this you can change squid.conf from:
 sslcrtd_program security_file_certgen -s /var/lib/ssl_db -M 32MB
...to...
 sslcrtd_program security_file_certgen

...and it will operate without the disk cache, generating certs fresh every time.

* Remove Ssl::CertificateDb::IsEnabledDiskStore()
 Make the CertificateDb temporary objects dynamically allocated instead.

* Do command line checks in main() not the CertificateDb object.
 This avoids a risky constructor exception and simplifies validity testing of parameters.

* Update man(8) documentation

 The helper version is now 1.1. A minor version bump since it is being kept compatible with
installations using 1.0 properly but new feature available.

 Also simplify the command line SYNOPSIS and incomplete mention of sslcrtd_* squid.conf directives.