[PATCH 3 of 3] exewrapper: add comments about PYTHONHOME

[Adrian Buehlmann]

# HG changeset patch
# User Adrian Buehlmann <adrian at cadifra.com>
# Date 1444818229 -7200
# Node ID cc306e37fbaf8cf45b23dd1a7467daf89607376e
# Parent  0bda366cf908c3ed6b67efed9d648efb3066bd78
exewrapper: add comments about PYTHONHOME

This has been a repeating source of confusion for users of HackableMercurial.

Note that users of HackableMercurial should *not* and are *not* expected to set
PYTHONHOME.

diff --git a/mercurial/exewrapper.c b/mercurial/exewrapper.c
--- a/mercurial/exewrapper.c
+++ b/mercurial/exewrapper.c
@@ -67,10 +67,19 @@
 	}
 
 	pydll = NULL;
+	/*
+	We first check, that environment variable PYTHONHOME is *not* set.
+	This just mimicks the behavior of the regular python.exe, which uses
+	PYTHONHOME to find its installation directory (if it has been set).
+	Note: Users of HackableMercurial are expected to *not* set PYTHONHOME!
+	*/
 	if (GetEnvironmentVariable("PYTHONHOME", envpyhome,
 				   sizeof(envpyhome)) == 0)
 	{
-		/* environment var PYTHONHOME is not set */
+		/*
+		Environment var PYTHONHOME is *not* set. Let's see if we are
+		running inside a HackableMercurial.
+		*/
 
 		p = strrchr(pyhome, '\\');
 		if (p == NULL) {