Start server process in dir where cmd was called

When a Spring server boots, it maintains its directory
for the duration of its life-cycle. This means that if you've changed
directories and run a Spring command, the process will start within the
context of the original directory.

This is problematic in the use case of engines, where an engine command
may be run from the context of the host application, and then run again
from the engine directory. In this scenario, the process will assume its
working directory is the host application instead of the engine.

The solution proposed here is to change the current directory to where
the Spring command was called from. The directory is taken from ENV['PWD']

lib/spring/application.rb

@@ -172,6 +172,11 @@ def serve(client)
         end
       end
 
+      # Ensure we boot the process in the directory the command was called from,
+      # not from the directory Spring started in
+      original_dir = Dir.pwd
+      Dir.chdir(env['PWD'] || original_dir)
+
       pid = fork {
         Process.setsid
         IGNORE_SIGNALS.each { |sig| trap(sig, "DEFAULT") }
@@ -237,6 +242,7 @@ def serve(client)
       # (i.e. to prevent `spring rake -T | grep db` from hanging forever),
       # even when exception is raised before forking (i.e. preloading).
       reset_streams
+      Dir.chdir(original_dir)
     end
 
     def terminate