libwebsockets

mbedtls and polarssl first part

polarssl is the old name for mbedtls.  Unfortunately the two are confused in eg,
Fedora.  For our purposes, polarssl or mbedtls < 2.0 has includes in
/usr/include/polarssl and polarssl_ apis and we call that "polarssl".

polarssl or mbedtls >=2.0 has includes in /usr/include/mbedtls and mbedtls_ apis,
we call that "mbedtls".

This has to be spelled out clearly because eg Fedora has a package "mbedtls" which
is 1.3.x and has the polarssl_ apis and include path.  We will deal with that as
"polarssl" despite the package name then.

This patch lets you use LWS_USE_POLARSSL or LWS_USE_MBEDTLS and set the include and
library path like this

cmake .. -DLWS_USE_POLARSSL=1 -DLWS_POLARSSL_INCLUDE_DIRS=/usr/include -DLWS_POLARSSL_LIBRARIES=/usr/lib64/libmbedtls.so.9

This patch adds the cmake support and adapts [private-]libwebsockets.h but doesn't
modify the apis in ssl[-*].c yet.

Signed-off-by: Andy Green <andy@warmcat.com>