Back out of a recent policy change (Mark Hammond disagreed).

The registry always comes first and the default is always appended.

PC/getpathp.c

@@ -164,17 +164,6 @@ search_for_prefix(argv0_path, landmark)
 #define BUILD_LANDMARK "PC\\getpathp.c"
 #endif
 
-static int
-prefixisbuilddir()
-{
-	int n = strlen(prefix);
-	int ok;
-	join(prefix, BUILD_LANDMARK);
-	ok = exists(prefix);
-	prefix[n] = '\0';
-	return ok;
-}
-
 #include "malloc.h" // for alloca - see comments below!
 extern const char *PyWin_DLLVersionString; // a string loaded from the DLL at startup.
 
@@ -364,7 +353,6 @@ calculate_path()
 		envpath = NULL;
 
 #ifdef MS_WIN32
-	if (!prefixisbuilddir()) {
 	/* Are we running under Windows 3.1(1) Win32s? */
 	if (PyWin_IsWin32s()) {
 		/* Only CLASSES_ROOT is supported */
@@ -374,7 +362,6 @@ calculate_path()
 		machinepath = getpythonregpath(HKEY_LOCAL_MACHINE, FALSE);
 		userpath = getpythonregpath(HKEY_CURRENT_USER, FALSE);
 	}
-	}
 #endif
 
 	/* We need to construct a path from the following parts.
@@ -404,8 +391,6 @@ calculate_path()
 	bufsz += strlen(PYTHONPATH) + 1;
 	bufsz += strlen(argv0_path) + 1;
 #ifdef MS_WIN32
-	if (userpath || machinepath)
-		bufsz = 0; /* Reset! */
 	if (userpath)
 		bufsz += strlen(userpath) + 1;
 	if (machinepath)
@@ -453,10 +438,6 @@ calculate_path()
 		*buf++ = DELIM;
 		free(machinepath);
 	}
-	if (userpath || machinepath) {
-		buf[-1] = '\0';
-		return;
-	}
 #endif
 	if (pythonhome == NULL) {
 		strcpy(buf, PYTHONPATH);