Improved hostname detection - initial changes

[robertpeteuil]

These updates improve the hostname detection in the shell integration script.

This pull consists of two commits:

• the first is for OpenBSD, and corrects hostname detection by assigning the hostname with cat /etc/myname instead of hostname -f issue #4225
• the second is for Linux hosts (without domains specified), and adjusts their hostname value for proper function in mDNS environments issue #4194

I've made a Google Docs Spreadsheet which summarizes the results of different hostname identification methods on a variety of host types and linux distros.

The next step is to get these changes ported into the fish, tcsh, and zsh scripts.

[robertpeteuil]

I just realized that I should have submitted the fix for the OpenBSD issue directly to master, as it fixes a hard error and assigns the proper value.

Specifically it's commit 8da909961e3d7a1812836a9d0b45ecbe44b90c79

Let me know if you want me to resubmit it directly to Master, or if you want to cherry-pick it from this branch.

[gnachman]

I'm ok keeping the OpenBSD fix here; the fewer versions in the wild, the better. I expect we can get this launched pretty quickly. This looks fine to me. zsh is probably the easiest one to tackle next because its syntax is very close to bash.