build-sys: keep noninstallable tests in noinst_tests

Repeating all tests in noinst_PROGRAMS and TESTS is pointless.
This way it is also clearer which noinst_PROGRAMs are not
part of the test suite.
journal-gatewayd: unify two code paths

In preparation for adding more options, split out the option
handling code.
journal-gatewayd: SSL support

For now the certificates are passed around as options to the
program. This might not be the most convenient under "production",
but makes for fairly easy testing.
journal-gatewayd: redirect microhttpd messages to journal

A prefix ("microhttpd: ") is added to the log lines to make it easy to
distinguish the source.
share/log: unify two code paths

Explicit zeroing is replaced with initialization to {0}.

No functional change.
share/log: skip file/line/func info if empty

The new microhttpd logger doesn't know this information. It is
better to log nothing than fake values.
journal-gatewayd: always log oom() in addition to returning error
journal-gatewayd: allow pipelining

The request must not be answered immediately (at first call to
response_handler()), but on the second. This is also important
for authentication, which cannot be performed on the first call.

Before:

% wget -O/dev/null -S https://localhost:19531/
--2012-11-28 18:29:43--  https://localhost:19531/
Resolving localhost (localhost)... 127.0.0.1
Connecting to localhost (localhost)|127.0.0.1|:19531... connected.
HTTP request sent, awaiting response...
  HTTP/1.1 301 Moved Permanently
  Connection: close
  Content-Length: 87
  Location: /browse
  Content-Type: text/html
  Date: Wed, 28 Nov 2012 17:29:44 GMT
Location: /browse [following]
--2012-11-28 18:29:43--  https://localhost:19531/browse
Connecting to localhost (localhost)|127.0.0.1|:19531... connected.
HTTP request sent, awaiting response...
  HTTP/1.1 200 OK
  Connection: close
  Content-Length: 23260
  Content-Type: text/html
  Date: Wed, 28 Nov 2012 17:29:44 GMT
Length: 23260 (23K) [text/html]

After:

% wget --no-check-certificate -O/dev/null -S https://localhost:19531/
--2012-11-28 18:30:05--  https://localhost:19531/
Resolving localhost (localhost)... 127.0.0.1
Connecting to localhost (localhost)|127.0.0.1|:19531... connected.
HTTP request sent, awaiting response...
  HTTP/1.1 301 Moved Permanently
  Content-Length: 87
  Location: /browse
  Content-Type: text/html
  Date: Wed, 28 Nov 2012 17:30:05 GMT
Location: /browse [following]
--2012-11-28 18:30:05--  https://localhost:19531/browse
Reusing existing connection to localhost:19531.
HTTP request sent, awaiting response...
  HTTP/1.1 200 OK
  Content-Length: 23260
  Content-Type: text/html
  Date: Wed, 28 Nov 2012 17:30:06 GMT
Length: 23260 (23K) [text/html]
journal-gatewayd: return nice error on unsupported methods

Returns "HTTP/1.0 406 Not Acceptable" instead of silently
closing the connection.
journal-gatewayd,man: document new HTTPS options