google: disable compression when curl is not available

This is a slightly hacky workaround for
https://github.com/google/google-api-php-client/issues/59 .
There's a bug in the Google library which makes it go nuts on
file uploads and transfer *way* too much data if compression is
enabled and it's using its own IO handler (not curl). Upstream
'fixed' this (by disabling compression) for one upload
mechanism, but not for the one we use. The bug doesn't seem to
happen if the google lib detects that curl is available and
decides to use it instead of its own handler. So, let's disable
compression, but only if it looks like the Google lib's check
for curl is going to fail.