fix(travis): add users/groups for wheel and portage to try to fix test envs
test(travis-ci): create wheel/portage groups first
test(travis-ci): don't force a specific wheel GID

The GID 10 already exists in travis-ci envs.
fix(eapi-bash): fix positional parameter string compares

It appears that when unquoted, ${*} and $* are treated differently
within double square brackets, probably due to nuances in pattern
matching and/or IFS handling.
fix(eapi-bash): use correct variable name

This fixes the absence of --disable-dependency-tracking and
--disable-silent-rules parameters for EAPI 4 and 5 in certain cases.
style(eapi-bash): combine unnecessary, extra logical expressions
style(eapi-bash): use globbed matches instead of substrings

Slightly easier to read in certain cases and slightly faster than
substring extraction/matching.
style(eapi-bash): use globbed matching instead of pattern substitution

Easier to read and fixes cases where arguments containing a string such
as "--libdirt" would have caused a false positive for the related
"--libdir" expression.
style(eapi-bash): simplify duplicate slash stripping for --libdir args

The __strip_duplicate_slashes function comes straight from portage.
fix(eapi-base): update func don't export list
feature(*): initial EAPI 6 support work
feature(eapi6): add stubs for various eapi6 functions

We should figure out a way to dynamically build a list of export blocks
for EAPI dependent functions, i.e. we shouldn't block exports from
eclasses for similarly named functions but instead override them with
internal PM implementations when EAPI provided functionality comes into
existence.

The current method involves explicitly adding the related functions to
the INTERNAL_FUNCS list the only current affected function being "usex"
that is defined in EAPI 5 and in the eutils.eclass for EAPI < 5. This
requires us to track implementations within eclasses which can be
problematic.