Allow CURL constant names

[Nyholm]

This will fix #71

[dbu]

is there something to check if a constant exists? imho an exception on nonexisting constant would be in order.

and s/contantValue/constantValue ;-)

[Nyholm]

If the constant does not exist constant() will return null.

Question: is it true that the only config parameters to the curl client are integers or constants named "CURL*"? If so, we should throw a exception.

[dbu]

according to http://php.net/manual/en/function.curl-setopt.php it must be int. so either it already is an int here, or its a constant. maybe we could do

if (!is_int($key)) {
    $constantValue = constant($key);
    if (null === $constantValue) {
        throw... $key is not an integer or a CURL constant.
    }
    unset...,
    $config[$constantValue] = $value;
}

[dbu]

not sure if we should force the constants to start with CURL - maybe there could be a reason to have some other constant that does not start with CURL.

is constant() case sensitive?

[sagikazarmark]

Invalid constants (integers) will end up in an error upon setopt anyway.

[Nyholm]

Okey. Then I'm safe to assume that everything that comes in is either an Int or a name of a constant. If the constant is not defined I'll throw an exception. If the Int is invalid CURL will throw an exception

[sagikazarmark]

If the Int is invalid CURL will throw an exception

Setopt triggers an error IMO, but this is something that should be handled in the cURL client anyway.

[Nyholm]

Thank you for the feedback. I've updated the PR accordingly.

[dbu]

awesome, thanks!

[Nyholm]

Thank you for merging.