disable Curl verbose mode

[Yaribz]

fix #58

[p2004a]

This particular verbose is very helpful for debugging, so I don't want to disable it unconditionally always.

Either:

• disable only when disable-loggins is set
• add option to enable at runtime

[Yaribz]

I thought it was a mistake (according to the commit messages, as explained in #58 ), and that the debug messages weren't supposed to be printed anymore. I was just trying to restore the expected behavior. I don't plan to add new features in pr-downloader, so if current behavior is already the expected one then all is good (I have already worked around it in SPADS anyway).