test: make sure '\' characters in a string are escaped to \\ so that the regexp works

fix: use super() properly to ensure that these classes are initialised as expected.

test: test for make_engines that are aliases referring to a sequence of variants.

fix: checkcomp filter formatting updates from Samu Sillanpaa. This is a custom filter for helium scanlog's missing files-per-component reporting.

fix: filterwhatcomp and filtercheckcomp - correctly strip absolute directory and replace with EPOCROOT on windows.

fix: failure of make engine test when a make engine alias contains a modifier. There can be more than one variant per alias via "." e.g. make.extrastuff where make and extrastuff are variants.

Fix up file testing with checkwhatcomp and make epocroot driveletter stripping case insensitive.

FilterCheckComp - checking file existence by component

Merge

release: notes for sbs_filter-related changes

Tests cor check and whatTests cor check and what

fix: make filters work with new default python fix: Make Check filter actually check stuff when run from the filter

Retain MakeEngine class API. Why not?

review comments, dates, test ids

Merge