OpenSystemsDevelopment / qpdf

The faulty code was only used during explicit checks of linearization
data.  Those checks are not part of normal reading or writing of PDF
files.

Better sanity check inputs to bit stream reader

4.2.0 was binary incompatible in spite of there being no deletions or
changes to any public methods.  As such, we have to bump the ABI and
are fixing some API breakage while we're at it.

Previous 4.3.0 target is now 5.1.0.

This is a cosmetic change since both are accepted.

Detect a missing page range and assume 1-z.

Thanks to Jiri Popelka from Red Hat for sending the output of a
Coverity run over qpdf.

s/Controls handing of object streams./Controls handling of object streams./

Space rather than newline after xref, missing /ID in trailer for
encrypted file.  This enables qpdf to handle some files that xpdf can
handle.  Adobe reader can't necessarily handle them.

Bug fixes for 4.2.0 force additional interfaces, so move most of the
4.2.0 items to 4.3.0.

Even though this case is not valid according to the spec, it has been
seen, and caused an internal error.

Rework QPDFWriter to always track old object IDs and QPDFObjGen
instead of int, thus not discarding the generation number.  Switch to
QPDF::getCompressibleObjGen() to properly handle the case of an old
object eligible for compression that has a generation of other than
zero.

In internal code and examples, replace calls to getObjectID() and
getGeneration() with calls to getObjGen() where possible.

This is safer than getObjectID() and getGeneration() for many uses.

Most Linux distributions include qpdf now, so there is no need to
distribute our own spec file.

Versions prior to 4.6 didn't allow gcc diagnostic pragmas with push
and pop and to appear anywhere in the file.  Just let the warning be
there for those versions.