pycurl: make doc and version strings const and read-only

Signed-off-by: Oskari Saarenmaa <os@ohmu.fi>
pycurl: make internal functions static

Signed-off-by: Oskari Saarenmaa <os@ohmu.fi>
pycurl.c: fix curl_easy_getinfo(CURLINFO_PRIVATE) argument type

Signed-off-by: Oskari Saarenmaa <os@ohmu.fi>
setup.py: detect ssl variant using ctypes/curl_version

curl-config --libs won't necessarily show the used SSL library,
try to grab it from curl version string instead.

Signed-off-by: Oskari Saarenmaa <os@ohmu.fi>