refs #409:

 * always use Crockford's JSON module (renamed to JSON2) to workaround broken "native implementations"
 * add JSON unit tests
 * revert [3893] and [3900]; rewrite getVisitorId() per comment:80
 * refactor browser feature detection for fingerprinting (used to generate uuid)
 * setDomains() now takes either '*.domain' or '.domain'
 * Safari emits warnings for Content-Length and Connection as "unsafe headers" in XHR POST request

refs #1984:
 * partially revert [3882] in order for the unit tests to run
 * fix inconsistency in getCustomVariable() depending on whether it is loaded from memory or from a cookie

refs #2078 Webkit bug ("Failed to load resource") when link target is the current window/tab
 * requires further discussion because the workaround may not be desirable behavior, i.e.,
{{{
if ((new RegExp('WebKit')).test(navigatorAlias.userAgent)
    && (!sourceElement.target.length || sourceElement.target === '_self')
    && linkType === 'link')
{
    // open outlink in a new window
    sourceElement.target = '_blank';
}
}}}


git-svn-id: http://dev.piwik.org/svn/trunk@3939 59fd770c-687e-43c8-a1e3-f5a4ff64c105