change verbiage stating exact compliance with RFC-1738

change verbiage stating exact compliance with RFC-1738

As long as we aren't using urlparse() to parse URLs,
we are not RFC-1738 compliant.   As we accept underscores
in the scheme and not dashes or dots, we are not
RFC-1738 compliant, so emulate language like
that of PostgreSQL [1] that we "generally follow" this
scheme but include some exceptions.

[1] https://www.postgresql.org/docs/current/libpq-connect.html#id-1.7.3.8.3.6
Fixes: #8519
Change-Id: I2d7e55d9df17aed122cebb2c4c315f56c06a3da5