Allow managing pkgset under local folder.

While replacing pakcageset name with "--local", the packageset
information will be managed under some/local/repo/.gvm_local folder, and
add the root path of repository as the first path in GOPATH and PATH.
This makes the repository more portable since we don't store all the
go-installed package files under $HOME/.gvm .

The repository root path for gvm is definded as $PWD while
"pkgset create --local" . When "pkgset list" under some configured local
repository, it will list the root path as the first packageset, and
marked with "L".

scripts/function/find_local_pkgset

@@ -0,0 +1,19 @@
+function find_local_pkgset
+{
+    local TOPFILE=.gvm_local
+    if [ -d $TOPFILE ] ; then
+        PWD= /bin/pwd
+    else
+        local HERE=$PWD
+        T=
+        while [ \( ! \( -d $TOPFILE \) \) -a \( $PWD != "/" \) ]; do
+            \cd ..
+            T=`PWD= /bin/pwd`
+        done
+        \cd $HERE
+        if [ -d "$T/$TOPFILE" ]; then
+            echo $T
+        fi
+    fi
+}
+