This fixes `hub -C mydir merge <URL>` and other commands that might be
invoked with git global arguments by ensuring that those global
arguments are also fowarded to any accompanying `git` commands within
`Before()` and `After()` chains.

For git commands that are extended by hub, such as `git remote`, the
final git command would get executed without the git global flags
provided when executing hub in the first place.

This most notably broke the usage of `-C <dir>` flag.

Avoids mutating `globalFlags` until a match has actually been found.

We used to recognize git global flags based on a hardcoded list.
Whenever git added more global flags, we didn't support them in hub
until we updated the list.

Now, treat all flags coming before the subcommand as global flags. These
are the rules:

1. Initially, every argument except `--help` and `--version` that starts
   with a `-` is considered to be a global flag.

2. Additionally, `-c` and `-C` flags have a value.

3. When an argument appears that doesn't match the above rules, assume
   that it's the git subcommand and stop global args parsing.

`Args.InsertParam` panics about index out of bound if the index is larger than param size. These changes reset the index to param size for such case. This is equivalent to appending new items to the end.

This fixes #812.

Parse more global flags from by following https://github.com/github/hub/blob/1.12-stable/lib/hub/commands.rb#L961-L995

https://github.com/github/hub/issues/698