In the recent refactoring of the HTTPClient, a problem with certain
systems was reintroduced. On these systems a select() call always
waits for a timeout on the first call before working properly on the
second call.

This patch reintroduces the shorter timeouts with usleep rate limiting
again.

Since this bug is not reproducible on other systems it can't be unit
tested unfortunately.

The included test cases currently expect a squid at localhost:3128

Reading from a socket is handled by functions that encapsulate the error
handling and timeout conditions.
_readData reads blocks of data.
_readLine reads a single line.

This is the first step in refactoring the socket reader to be more
resilient and easier to debug.

The previous regexp approach failed for empty headers.

On certain environments, stream_select might produce temporary errors
when file descriptors are running scarce.

This changes the HTTP stream to blocking while writing to the stream
using select() to handle timeouts. Addtionally, wwriting is done in 4k
block now (as it is done with reading).

This is supposed to fix a problem with writing to a SSL stream that is
not quite ready.

Reading from the stream continues to be non-blocking as before.

since we don't use setter/getters for the other options it doesn't make
sense to have them for the keep-alive function

As soon as something goes wrong while querying a http server
do not reuse the same connection again, its state is undefined.

In addition, check the connection for feof() before reusing it.

Using a static context for the connection pool allows connection
reuse throughout the whole application without additional changes
in other places.

The DokuHTTPClient is now able to keep connections alive. This
feature is enabled by default. It can be disabled with
    $client->setKeepAlive(false);
and asked with
    $client->isKeepAlive();.

As of VIM 7.3 it is no longer possible to specify the encoding in the
modeline. This gives an error message whenever such a file is opened,
thus this commit removes the enc setting from the modeline.

Some servers send a content-encoding for gzip files but do not encode
the content themselves. This is IMHO wrong, this patch detects this
and ignores the header. The request will return true but set a
warning message in $this->error