ISSUE-42: @src attribute

Hi all,

For some reason, ISSUE-42 does not seem to be marked resolved, even
though I believe we have resolved it to everyone's satisfaction.

The resolution I believe we came to, which the syntax doc and test cases
support, is:

"@src on IMG behaves just @href and @resource, and it is overridden by
@href and @resource, in that order."

Please vote +1 or -1 ASAP.

-Ben