- Allow the user to use PKG_CONFIG but not PKGCONFIG.

Background:

Last week in 14d5a86b a change was made to allow the user to set the
PKGCONFIG variable. Today in 72d99f2e I supplemented that to allow the
more common PKG_CONFIG as an alternative if PKGCONFIG is not set.

Neither of those changes worked as expected because PKGCONFIG is
occasionally reset in configure and by the CURL_CHECK_PKGCONFIG macro.
Instead in this commit I take the approach that the user may set
PKG_CONFIG only.

- If mingw ssl make sure -lgdi32 comes after ssl libs

- Allow PKG_CONFIG to set pkg-config location and options

Bug: https://github.com/bagder/curl/pull/501
Reported-by: Kang Lin

Global private symbols MUST start with Curl_!

Closes #505

This allows FTP transfers with growing (or shrinking) files without
causing a transfer error.

Closes #480

... and add a little example of what the weight actually means. "Relative
proportion of bandwidth".

Removed wrong assert()s

The 'conn' passed in as userdata can be used and there can be other
sessionhandles ('data') than the single one this checked for.

CURLOPT_STREAM_DEPENDS

CURLOPT_STREAM_DEPENDS_E

CURLOPT_STREAM_PRIORITY

Closes #502

- Add a VPATH-statement for the vtls/*.c files.

- Due to 'vtls/*.c', remove that subdir part from $(OBJECTS).

... noticed with mbedTLS.

closes #496

- Use CURL_BINARY_DIR instead of CMAKE_BINARY_DIR.

When including CURL using add_subdirectory the variables
CMAKE_BINARY_DIR and CURL_BINARY_DIR hold different paths.

Closes https://github.com/bagder/curl/pull/488
Closes https://github.com/bagder/curl/pull/498

For example in test 1136

... that's for the library only.

... to make test 1014 work again after e77b5b74.

Using a last cache linked-list improves the performance of easysrc
generation.

Bug: https://github.com/bagder/curl/issues/444
Ref: https://github.com/bagder/curl/issues/429

Closes #452

Use libpsl to check the domain value of Set-Cookie headers (and cookie
jar entries) for not being a Publix Suffix.

The configure script checks for "libpsl" by default. Disable the check
with --without-libpsl.

Ref: https://publicsuffix.org/
Ref: https://github.com/publicsuffix/list
Ref: https://github.com/rockdaboot/libpsl

bug introduced by 18691642.

Closes #493

introduced in c6aedf68. It needs to be CURLM_STATE_LAST big since it
must hande the range 0 .. CURLM_STATE_MSGSENT (18) and CURLM_STATE_LAST
is 19 right now.

Reported-by: Dan Fandrich
Bug: http://curl.haxx.se/mail/lib-2015-10/0069.html

... and assign it from the set.fread_func_set pointer in the
Curl_init_CONNECT function. This A) avoids that we have code that
assigns fields in the 'set' struct (which we always knew was bad) and
more importantly B) it makes it impossibly to accidentally leave the
wrong value for when the handle is re-used etc.

Introducing a state-init functionality in multi.c, so that we can set a
specific function to get called when we enter a state. The
Curl_init_CONNECT is thus called when switching to the CONNECT state.

Bug: https://github.com/bagder/curl/issues/346

Closes #346

... and allow it to get set by a caller easier.

Reported-by: Rainer Jung
Bug: http://curl.haxx.se/mail/lib-2015-10/0035.html

sk_X509_pop will decrease the size of the stack which means that the loop would
end after having added only half of the certificates.

Also make sure that the X509 certificate is freed in case
SSL_CTX_add_extra_chain_cert fails.

It makes it a clearer message for developers reaching that point without
the necessary support.

Thanks-by: Jay Satiro

Closes #78

follow-up from 6f8ecea0

... as in the polarssl TLS backend for example it uses memory functions.