.netrc support

[eribertomota]

From Debian[1]:

Axel should try to use the .netrc file when trying to login to an FTP server.

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=127074

Regards,

Eriberto

[davidpolverari]

I would like to try to implement this feature, as I already have implemented a (somewhat naive, but working) simple .netrc parser in a few lines. But before I finish that, I would like the feedback on some points:

• I thought about only enabling .netrc parsing through a command-line option, not as a default behavior, as not to break the existing user experience, scripts, etc. What do you think about it?
• The long option could be something along the lines of --netrc[=filename]. If the option was used, it would parse the $HOME/.netrc file or an optional user-provided filename. I don't know which letter would be more appropriate for the short option. Suggestions are welcome.
• Other doubt is whether the code should be compiled by default along the rest of axel, or be conditionally compiled using the pre-processor. I don't think it will have such an impact on code size, but I wanted to know the opinions on it.

Thanks in advance.

[davidpolverari]

I submitted a PR that implements the feature. I intend to enhance some points of the implementation in the future, but for now it seemed to work for me. Tests are welcome.

I purposefully didn't change any of the .po files because of my ignorance of internationalization issues, so the new messages added to print_help() do not appear at the moment, in spite of the options being functional.