schannel: Code cleanup and bug fixes

curl_sspi.c: Fixed mingw32-gcc compiler warnings
curl_sspi.c: Fixed length of error code hex output

The hex value was printed as signed 64-bit value on 64-bit systems:
SEC_E_WRONG_PRINCIPAL (0xFFFFFFFF80090322)

It is now correctly printed as the following:
SEC_E_WRONG_PRINCIPAL (0x80090322)

curl_sspi.c: Fallback to security function table version number
Instead of reporting an unknown version, the interface version is used.

curl_sspi.c: Removed SSPI/ version prefix from Curl_sspi_version
curl_schannel: Replaced static buffer sizes with defined names
curl_schannel.c: First brace when declaring functions on column 0
curl_schannel.c: Put the pointer sign directly at variable name
curl_schannel.c: Use structs directly instead of typedef'ed structs
curl_schannel.c: Removed space before opening brace
curl_schannel.c: Fixed lines being longer than 80 chars