osx: run postinstall configure cmd as current user

In the macOS installer postinstall script we run the `configure` command
to get GCM to configure the current user's credential helper as GCM.

However, the postinstall script is often run as root (because that's how
`installer` works out of the box), meaning although GCM will be writing
to the ~/.gitconfig file, it will be doing so from a process running as
root.

To avoid having root take ownership of ~/.gitconfig we run `sudo -u` to
run the `configure` command as the real user (not root).

src/osx/Installer.Mac/scripts/postinstall

@@ -30,7 +30,11 @@ fi
 mkdir -p /usr/local/bin
 /bin/ln -Fs "$INSTALL_DESTINATION/git-credential-manager-core" /usr/local/bin/git-credential-manager-core
 
-# Configure GCM for the current user
-"$INSTALL_DESTINATION/git-credential-manager-core" configure
+# Configure GCM for the current user (running as the current user to avoid root
+# from taking ownership of ~/.gitconfig)
+if [ "${COMMAND_LINE_INSTALL}" = "" ]
+then
+    sudo -u ${USER} "$INSTALL_DESTINATION/git-credential-manager-core" configure
+fi
 
 exit 0

src/osx/Installer.Mac/uninstall.sh

@@ -10,9 +10,9 @@ then
 	exit $?
 fi
 
-# Unconfigure
+# Unconfigure (as the current user)
 echo "Unconfiguring credential helper..."
-"$GCMBIN" unconfigure
+sudo -u `logname` "$GCMBIN" unconfigure
 
 # Remove symlink
 if [ -L /usr/local/bin/git-credential-manager-core ]