syscall: make Getwd check $PWD on OS X

[rsc]

On OS X, if you cd /tmp and call os.Getwd (which calls syscall.Getwd) it returns
"/private/tmp".

In Go 1.2 and earlier it returned "/tmp", because it used the "check
$PWD, and then walk .. repeatedly" algorithm. CL 12349044 changed it to use
getattrlist, so in Go 1.3 it returns "/private/tmp" (/tmp is a symlink to
/private/tmp).

The C library routine getwd returns "/tmp". I know this because liblink in C
sees "/tmp" and liblink in Go sees "/private/tmp".

I think we should probably add the $PWD check to OS X's syscall.Getwd (or else move it
up above the ImplementsGetwd check in package os's Getwd, but changing OS X alone is the
more conservative change).

CL 118970043 does this. We just have to decide if that's what we want to do.

[ianlancetaylor]

Comment 1:

I vote for moving the PWD check to the start of os.Getwd.  That pretty much always the
right thing to do in practice.  It's less conservative but I can't think of anything
likely to break.

Labels changed: added repo-main.

[rsc]

Comment 2:

This may be worth 1.3.1. Not sure.

Labels changed: added release-go1.3.1, removed release-go1.4.

[gopherbot]

Comment 3:

CL https://golang.org/cl/118970043 mentions this issue.

[rsc]

Comment 4:

This issue was closed by revision 6cee4d3.

Status changed to Fixed.

[ianlancetaylor]

Comment 5:

That CL broke Windows; see https://golang.org/cl/119600043/ for a (ugly) fix.

[rsc]

Comment 6:

No one is reporting this problem except me.
Delaying to 1.4.

Labels changed: added release-go1.4, removed release-go1.3.1.