Minor vl-lint bugfixes

  - We were eliminating unused variables before argresolve, which could lead us
    to not realize that a variable was used in SystemVerilog .*- and .foo-style
    port connections.  This could cause spurious and confusing warnings about
    .* style connections that appeared to be missing variables.

  - Clean up new blank arg warning.  It had been printing the raw port
    structure, which was ugly.
vl: major speedups to a couple of lint transforms

The new vl-context stuff was, in some cases, extremely expensive, so this is
just some reworking things to avoid that expensive.  Also sped up duplicate
expression checking in the leftright check.
Minor vl-lint bugfixes

  - We were eliminating unused variables before argresolve, which could lead us
    to not realize that a variable was used in SystemVerilog .*- and .foo-style
    port connections.  This could cause spurious and confusing warnings about
    .* style connections that appeared to be missing variables.

  - Clean up new blank arg warning.  It had been printing the raw port
    structure, which was ugly.
Merge remote-tracking branch 'remotes/xb/master'