#614 Complie breaks with "unresolved external symbol" errors (for SSL objects)

[NSK]

If there is no OpenSSL available, Opal and PTLib compile fine, but when the consumer application tries to compile, unresolved external symbol errors occur for the objects PSSLCipherContext, PSHA1Context and PSSLContext.

This is because of pssl.cxx contain correct compile conditions on the P_SSL symbol, but the header files lacks these.

After adding these conditions to the files pssl.h and shttpsvc.h, the errors are gone.