Looks good

Made getHeader() case-insensitive.

Leaving open for Jan to look at, since he knows Horde_Http code better 
than I do.

Changes have been made in Git (master):

commit 25a839f2bb73c3ab7eae5d14c9116e4ab7e54814
Author: Michael M Slusarz <slusarz@horde.org>
Date:   Thu Dec 4 11:24:25 2014 -0700

     [mms] Horde_Http_Base_Response#getHeader() is now 
case-insensitive for the header input (Bug #13736).

  framework/Http/lib/Horde/Http/Response/Base.php    |   45 ++++++++++++-------
  .../Http/lib/Horde/Http/Response/Peclhttp.php      |    7 ++-
  .../Http/lib/Horde/Http/Response/Peclhttp2.php     |    7 ++-
  framework/Http/package.xml                         |    4 +-
  4 files changed, 38 insertions(+), 25 deletions(-)

http://github.com/horde/horde/commit/25a839f2bb73c3ab7eae5d14c9116e4ab7e54814

This is just flat-out wrong, considering that HTTP headers are case 
insensitive.

We have Horde_Support_CaseInsensitiveArray to handle this, for example.

FreeBusy.php uses the Horde Http Client class to retrieve information 
and queries the content type with

lib/FreeBusy.php:188
             if ($response->code == 200 && $data = $response->getBody()) {
                 // Detect the charset of the iCalendar data.
                 $contentType = $response->getHeader('Content-Type');

However, the parameter to getHeader() is case-sensitive _and_ 
lower-case, see below.

Horde_Http_Response_Base:

/**
      * Returns the value of a single response header.
      *
      * @param string $header  Header name to get ('Content-Type',
      *                        'Content-Length', etc.). This is case sensitive.
      *
      * @return string HTTP header value.
      */
     public function getHeader($header)

in function _parseHeaders() line 82

             if (preg_match('|^([\w-]+):\s+(.+)|', $headerLine, $m)) {
                 unset($lastHeader);
                 $headerName = strtolower($m[1]);

====

So either it's a bug in getHeader(), because it does not lower-case 
the header name, or FreeBusy.php need to request the lower-case header 
name and the documentation of getHeader() should reflect it, too.