Allow testPreconditionRequiredStatusCode to run independently

Previously it required testPutRequiresIfMatch, which is only a SHOULD
requirement. Thus if you ran just the MUST group, the test would be
skipped.

This commit changes the test to determine if If-Match is required on its
own without running testPutRequiresIfMatch.

Fixes #41
fix two problems with testRelativeUriResolutionPut

1) The test should not fail if the PUT request fails. For instance, the
server might not accept arbitrary triples (in our case dcterms:title).
LDP does not require servers to accept any content. Skip the test if we
can't successfully PUT.

2) We are not correctly asserting that the modified resource has the
updated property.

Fixes #39
Merge pull request #43 from spadgett/master

Allow testPreconditionRequiredStatusCode to run independently