Add socket traffic stats to listsockets response

Not yet added to Web interface though.
Add traffic stats to listsockets webadmin table

Table is not displaying, however. Odd.
Add new columns to listsockets tmpl
Merge commit 'refs/pull/488/head' of github.com:znc/znc
Add CString::StartsWith and CString::EndsWith
The Listener of a RealListener is never NULL
Add URIPrefix listener option
Add prefix on redirects and strip it on requests
Prepend URIPrefix to web interface links

Prefix links in templates with URIPrefix and add the input field to the
Listener editor.

The URIPrefix is provided as a top-level template variable. All URIs
have been changed to have the prefix prepended.
Use absolute URIs in Redirect

Although most browsers seem to accept relative redirects, it is not
allowed by HTTP/1.1.

This commit changes relative URIs to absolute ones when redirecting.
Don't support relative redirects
Redirect to URIPrefix for paths outside the prefix
Set favicon URL to respect the prefix

When not specified, browsers tend to send favicon request to
/favicon.ico. This commit tells the browsers to look for it under the
URIPrefix.
Merge pull request #485 from uu1101/uriprefix

Allow serving the web interface under a subpath
Fix #480
Fix #138
Fix znc-buildmod

It failed to build some modules...

Thanks to kay45 for reporting this
webadmin: default uriprefix is "/"
configure: Give a reason for disabled features

This adds a short reason to the summary at the end of configure (for options
where it makes sense, e.g. not debug or ipv6).

Example:

  charset:      no (icu-uc not found via pkg-config)

Signed-off-by: Uli Schlachter <psychon@znc.in>
Merge pull request #496 from psychon/config-reasoning

configure: Give a reason for disabled features
configure: Add --enable/disable-charset

This override the auto detection. If --enable-charset is given, but icu can't be
found, configure will error out.

Signed-off-by: Uli Schlachter <psychon@znc.in>
Merge pull request #498 from psychon/configure-flag-for-charset

configure: Add --enable/disable-charset