www/{nginx,nginx-devel,freenginx}: 3rd-pary modules managemeht

Fix build and loading of the 3rd party gridfs module after the
devel/mongo-c-driver 2.x update.

The module config now obtains include and linker flags from
pkg-config instead of deriving them from the ports tree's
DISTVERSION. The previous approach ran a recursive make into
devel/mongo-c-driver on every make invocation, even with GRIDFS
unset, and derived the libbson include path from the mongo-c-driver
version although devel/libbson is a separate port with its own
DISTVERSION. Both directories happen to carry the same version
today, so the mismatch was not visible yet.

While here, add the missing assert.h include. The module calls
assert() without declaring it, which left an unresolvable symbol
"assert" in the shared object -- libc only exports __assert. Since
nginx dlopen()s modules with RTLD_NOW, load_module refused to load
the module at runtime.

Also correct a typo in one of the patch file names.

PR: 296604, 296605, 296606
Sponsored by: Netzkommune GmbH