Use hMainProc where appropriate, throughout.

* environ.cc (spenv::retrieve): Add debugging statements.
* pinfo.cc (set_myself): Don't call strace.hello if already stracing.
* strace.cc (strace): Move NO_COPY keyword so that it will actually take
effect.

winsup/cygwin/passwd.cc

@@ -168,7 +168,7 @@ read_etc_passwd ()
 	      cygsid tu, tg;
 	      DWORD siz;
 
-	      if (OpenProcessToken (GetCurrentProcess (), TOKEN_QUERY, &ptok))
+	      if (OpenProcessToken (hMainProc, TOKEN_QUERY, &ptok))
 	        {
 		  if (GetTokenInformation (ptok, TokenUser, &tu, sizeof tu,
 		                           &siz)