PHPC-534: Enable configure without SASL

[kaplanlior]

And fix some minor issues.

[derickr]

Any reason why you are changing the default from "yes" to "no" here?

[kaplanlior]

When the default is yes, it doesn't respect --with-mongodb-sasl=no . The macros keep changing it to yes.
That also makes auto to become yes (and making the other check no relevant).

[jmikola]

I can reproduce the behavior @kaplanlior mentioned above. On that note, I think we should make a similar change to --with-pcre-dir[=DIR].

FWIW, this doesn't appear to be discussed directly in the build docs. Their --with-example[=FILE] example would omit the "auto, (yes|no)" bit entirely. For our needs of having --with-mongodb-sasl default to auto if unspecified, but still respect "=no", Lior's solution seems to work nicely.

[jmikola]

I rebased this with additional changes (and a link to a corresponding JIRA ticket) in #197.