Merge branch 'ep/use-git-trace-curl-in-tests'

Update a few tests that used to use GIT_CURL_VERBOSE to use the
newer GIT_TRACE_CURL.

* ep/use-git-trace-curl-in-tests:
t5551-http-fetch-smart.sh: use the GIT_TRACE_CURL environment var
t5550-http-fetch-dumb.sh: use the GIT_TRACE_CURL environment var
test-lib.sh: preserve GIT_TRACE_CURL from the environment
t5541-http-push-smart.sh: use the GIT_TRACE_CURL environment var

diff --cc t/test-lib.sh
Simple merge