algebra: Add polyfactor0 to build

Not sure why it wasn't included, but it is now.
Add quick testcase for DenseUnivariatePolynomials.
tfsat.c: Handle cases of defined types appearing in embeddings
Add multivariate polynomials into the algebra library.

They've been sitting around for a while, and it's probably time they
got committed.  Note: I've done no testing beyond 'does it compile'

One small issue: there's a 'combine' method in alg_ezgcd which does not
have a definition, only a specification (I guess it was removed from the
original sources at some point).  This means multivariate gcd won't work
as it stands.
genfoam: Remove support for -Wold-hashcodes.

This was for older versions of axiom; I don't think it makes a massive amount
of sense to retain support for these, especially as the hashcode calculation
has changed.   Simplifies the code slightly too.
tfGetCatExportsFrParents wasn't dealing with lists correctly.
dnf/ablogic: DNF now supports simplification of expressions containing
negations.  Add test case
Plus a formatter for DNFs for easier debugging.
dnf/ablogic: Add some extra tests, and improve dnf debug output.
aldortest: noticed that the float test was failing.. fix is simple, so
made it.
absyn.c: Rework hash function to take care of Pretend, Restrict and Test.
Use in ablogic.. This way, conditions like prime?(p) will be matched with
prime?(p)$F

Add confirming assertion in sefo.c, and some tests.
tform.c: Small improvements to debug output.
Showexports.c: include condition in category output
syme.c: add missing fieldInfo for SYFI_ConditionContext. Also, be paranoid
and check during initialisation.
lib/ax0/test: Use $(DBG), cos everything else does.
Set libraryincdir in libfoamlib - makes %.gloop targets work properly
build: Make Tests.am depend on Makefile.am

This way, a change in Makefile.am (usually a new test) will filter into
Tests.am.  And so the test will run next build.
lib/ax0: axextend.as: ShouldHaveSegmentGenerator's condition was incorrect.

Basically, it is looking for S has with { coerce: I -> S }.  This should
be I -> %, as it is the form actually exported.
genfoam.c: gen0HasImport returns a Word, cast it back to a boolean
showexports: category pretty printing wasn't correct. fix
syme.c: As an optimisation, call tiSefo if possible before launching into
tiGetTopLevelTForm.  tiSefo is less heavyweight when determining the type
of an expression.