mbedtls and polarssl first part

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>