Fix exit-code pass-thru with nave use and add -o option to enable overriding default cURL flags

[niallo]

E.g. get silent output with

nave -o'-Lfs' install 0.8.0

[niallo]

Added another commit to fix bug with nave use:

without patch:

<nialljohiggins@mbp:nave>$ nave use 0.8.0 exit 1
Already installed: 0.8.0
using 0.8.0
<nialljohiggins@mbp:nave>$ echo $?
0

with patch:

<nialljohiggins@mbp:nave>$ sh nave.sh use 0.8.0 exit 1
Already installed: 0.8.0
using 0.8.0
failed somehow
<nialljohiggins@mbp:nave>$ echo $?
1

[isaacs]

Took the return value hiding, and changed to not do --debug.

Parsing options and overriding the curl opts seems weird and unnecessary to me.

In general, it's best to only have one feature per pull request. You can push different features to different branches to keep it more clear.

[niallo]

Thanks. Sorry about the multiple features in that pull request, will do branches next time.

Re: cURL opts. My use case is saving nave output. cURL's progress bar (-# option) does not gracefully handle non-TTY output fd and essentially spews garbage. To see what I mean, just redirect nave output to a file. Hopefully that convinces you :-)

Perhaps a better alternative to parsing options is using an environment variable? I'm not wedded to the getopt approach.