OpenSystemsDevelopment / qpdf

Use QPDFObjectHandle::isNameAndEquals, isDictionaryOfType and
isStreamOfType.

Accept empty string as type parameter in
QPDFObjectHandle::isDictionaryOfType and isStreamOfType
to allow for dictionaries with optional type.

Add methods isNameAndEquals, isDictionaryOfType, isStreamOfType

When adding a QPDFObjectHandle to an array or dictionary, if possible,
check if the new object belongs to the same QPDF. This makes it much
easier to find incorrect code than waiting for the situation to be
detected when the file is written.

Also improve behavior around direct vs. indirect resources.

This results in a performance penalty of 1% to 2% when replaceObject
and swapObjects are never called and a somewhat larger penalty if they
are called, but it's worth it to avoid very confusing behavior as
discussed in depth in qpdf#507.

There are lots of things with /Kids that are not pages. Repair the
pages tree, then do a reliable check.

Also fix a bug in checking consistency of length for stream data
providers. Length should not be checked or recorded if the provider
says it failed to generate the data.

Avoid calling finish() multiple times on the pipeline passed to
pipeContentStreams. This commit also fixes a bug in which qpdf was not
exiting with the proper exit status if warnings found while splitting
pages; this was exposed by a test case that changed.

Make some more methods in QPDFPageObjectHelper work with form
XObjects, provide forEach methods to walk through nested form
XObjects, possibly recursively. This should make it easier to work
with form XObjects from user code.

StreamDataProvider::provideStreamData now has a rich enough API for it
to effectively proxy to pipeStreamData.

Refactor removeUnreferencedResources to prepare for filtering form
XObjects.