curl segfault in debug callback triggered with CURLINFO_HEADER_OUT and size 0

bug: http://curl.haxx.se/bug/view.cgi?id=3511794

Simplified the code to remove the need for a separate "LIST <msg id>"
command handler and state machine and instead use the LIST command
handler for both operations.

Corrected character and line spacing and re-ordered list and retr
functions based on the order of their state machines.

Moved the server greeting response handling code from the statemach_act
functions to separate response functions. This makes the code simpler
to follow and provides consistency with the other responses that are
handled here.

Body data would be forwarded to the client application in both the RETR
and LIST commands even if CURLOPT_NOBODY was specified.

Original wording could lead users in thinking it tries to
somehow parse the filename for a date expression (like
news_2012_03_05.html). It never mentions that it actually
reads the mtime of the file in filesystem.

This allows building of libcurl on DOS using DJGPP 2.04 and Watt-32
sockets. I know there's already Makefile.djgpp, but I find this more
convenient since I'm used to using the ./configure script from other
platforms

The commit e650dbde that stripped off [brackets] from ipv6-only host
headers for the sake of cookie parsing wrongly incremented the host
pointer which would cause a bad free() call later on.

The refactoring of HTTP CONNECT handling in commit 41b02378 that
made it protocol independent broke it for the multi interface. This fix
now introduce a better state handling and moved some logic to the
http_proxy.c source file.

Reported by: Yang Tse
Bug: http://curl.haxx.se/mail/lib-2012-03/0162.html

Take in account that POSIX standard Issue 7 drops h_errno support. Now, we also
consider getaddrinfo() to be thread-safe when (_POSIX_C_SOURCE >= 200809L) or
(_XOPEN_SOURCE >= 700) independently of whether h_errno exists or not.

Use fopen() with "w" mode instead of "wt" to fix cygwin builds.

3 more bugs, 1 more contributor

Windows standard libraries are located in C:/Program Files/Microsoft
SDKs/[...]. They are already included in the default MSVC
LIBPATH. Hence, find_library(WSOCK32_LIBRARY wsock32) and
find_library(WS2_32_LIBRARY ws2_32) are not needed. They return the full
path to the libraries including spaces. Of course,
list_spaces_append_once will mangle the result and the build fails.

Bug: http://curl.haxx.se/bug/view.cgi?id=3494968