Fix testTokenChecks: add missing __FILE_FULL_PATH__

[wilzbach]

This should bump the coverage enormously as the testsuite aborted on an AssertionError before it could parse / lex any file in the coverage mode.

[codecov-io]

Codecov Report

Merging #151 into master will increase coverage by 74.33%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           master     #151       +/-   ##
===========================================
+ Coverage    7.13%   81.47%   +74.33%     
===========================================
  Files           7        7               
  Lines        4527     4528        +1     
===========================================
+ Hits          323     3689     +3366     
+ Misses       4204      839     -3365

Impacted Files	Coverage Δ
test/tester.d	100% <100%> (+7.54%)	⬆️
src/dparse/lexer.d	80.01% <0%> (+77.03%)	⬆️
src/std/experimental/lexer.d	83.72% <0%> (+83.72%)	⬆️
src/dparse/parser.d	87.46% <0%> (+87.46%)	⬆️
src/dparse/stack_buffer.d	87.5% <0%> (+87.5%)	⬆️
src/dparse/rollback_allocator.d	89.58% <0%> (+89.58%)	⬆️

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