Nelgin reported a weird error with a failed very large allocation for the
base/code argument to the FileBase constructor. There's no good reason
these strings were heap-allocated in the first place, so just change to
use a stack allocated variable instead. I don't know why this would fix
anything, but at least there's one less heap allocation and potential
for memory leak here.

Fix 2 bugs in js_update_file():
1. missing parenthesis (really?!? Caught by Coverity - sigh) in last
commmit caused attempt/failure/error to remove file after making any
updates. The removing is only supposed to happen when its necessary to
remove and re-add the file to the filebase (e.g. updating extended
description or auxdata).
2. Wrong filename used in 'removing' exception string.