Failing test case for --debug --standalone

This demonstrates that with the --standalone option the UMD prelude
is adding a source line to the output. Since browserify doesn't change
the source map generated by browser-pack, which accommodates its require
runtime preamble, the result is a source map with an off-by-one error in
generated line numbers.

Previously, I attempted to offload --standalone onto browser-pack, but it
can be easily handled by just asserting that the additional prelude not
consume an additional source line.
Trim the UMD prelude to preserve lineno

Since browser-pack generates a source map when the debug option is
used we don't want to cause an additional source line to be added
or we'll have to process and fix the mappings.

Fixes the failing test case introduced in the previous commit.

Closes #390 -- I think?
2.35.2