In CurlDownloader, use the global timeout (instead of a hardcoded 5-minute timeout)

[smokris]

CurlDownloader is hardcoded to a 5-minute timeout. When downloading a large file on a slow internet connection, it hits this timeout, then aborts and restarts the download from the beginning, and composer install is unable to make any progress.

This PR modifies CurlDownloader to use the global ProcessExecutor timeout (COMPOSER_PROCESS_TIMEOUT) instead. (COMPOSER_PROCESS_TIMEOUT defaults to 5 minutes, just like the hardcoded value in CurlDownloader, so the default behavior remains the same when that environment variable is not set.) With this PR, when I set COMPOSER_PROCESS_TIMEOUT to an appropriate value for my internet connection, composer install is able to complete successfully.

[Seldaek]

It's a valid point that this shouldn't be hardcoded, but IMO the process timeout isn't the way to change this. The default_socket_timeout ini setting is the closest thing we have to having this configurable in the past, so it now respects this too for curl transfers. I hope this lets you resolve your issue too.

[smokris]

Ah, that makes sense. With your commit, I confirmed that I'm able to increase the timeout by setting default_socket_timeout=3600 in my php.ini, which enables me to download large files here. Thanks!