VirtualResolutions minor update

[mahrud]

Quick update that fixes a few issues and adds some speedups.

• raised the limit of FourTiTwo for printing debug info
• added quick test for non-quasilinearity in LinearTruncations
• improved multigradedRegularity
• added new test for multigradedRegularity
• quickfix in VirtualResolutions
• fixed internal function plotRegion

One important change in Core:

• improved RingMap ** Module for modules without relations (e.g. an image module remain an image module)

[mahrud]

@mikestillman @DanGrayson currently RingMap Module only works for free modules and image modules while RingMap ** Module will convert any module to a cokernel module since it computes cokernel f presentation M.

Is there any reason why both RingMap Module and RingMap ** Module should not work for all modules by just applying the ring map to the generators and relations and creating an equivalent subquotient module?

This PR is changing RingMap ** Module to do as above, and I expected some test to fail if this was on purpose, but it doesn't seem to be the case:

M2/M2/Macaulay2/m2/ringmap.m2

Lines 200 to 219 in 060e16f

	RingMap Ideal := Ideal => (f, I) -> ideal f module I
	RingMap Module := Module => (f, M) -> (
	(S, R) := (target f, source f);
	if R =!= ring M then error "expected module over source ring";
	if M.?relations then error "ring map applied to module with relations: use '**' or 'tensor' instead";
	if M.?generators then image f M.generators
	else ( -- M is a free module
	d := degrees M;
	e := f.cache.DegreeMap \ d;
	-- use the same module if we can
	if R === S and d === e then M else S^-e)
	)
	-- misc
	tensor(RingMap, Module) := Module => {} >> opts -> (f, M) -> (
	if source f =!= ring M then error "expected module over source ring";
	subquotient(f ambient M,
	if M.?generators then f M.generators,
	if M.?relations then f M.relations))
	RingMap ** Module := Module => (f, M) -> tensor(f, M)

[mahrud]

@mikestillman I added a fix for the bug from David's email here.