Remove GOBIN in PATH dependency; don't assume cwd is $GOROOT/src

This change removes the necessity to have GOBIN in $PATH,
and also doesn't assume that the build is being run from
$GOROOT/src. This is a minimal set of necessary changes
to get Go to build happily from the FreeBSD ports
collection.

R=rsc
CC=golang-dev
https://golang.org/cl/171044
diff --git a/doc/install.html b/doc/install.html
index a378719..e736557 100644
--- a/doc/install.html
+++ b/doc/install.html
@@ -82,10 +82,9 @@
 </dt>
 <dd>
 	The location where binaries will be installed.
-	If you set <code>$GOBIN</code>, you need to ensure that it
-	is in your <code>$PATH</code> so that newly built Go-specific
-	command such as the compiler can be found during the build.
-	The default, <code>$HOME/bin</code>, may already be in your <code>$PATH</code>.
+	The default is <code>$HOME/bin</code>.
+	After installing, you will want to arrange to add this
+	directory to your <code>$PATH</code>, so you can use the tools.
 </dd>
 </dl>
 
@@ -204,9 +203,7 @@
 </p>
 
 <p>
-To build the Go distribution, make sure <code>$GOBIN</code>
-(or <code>$HOME/bin</code> if <code>$GOBIN</code> is not set)
-is in your <code>$PATH</code> and then run
+To build the Go distribution, run
 </p>
 
 <pre>