patch to make build.py run under linux

[JohnDenker]

This patch makes build.py work for me under linux.
The code should be self-explanatory.

commit 112273fce1ea8b015931e5df5fcc401d483b6a39
Author: John Denker <jsd@av8n.com>
Date:   Tue Sep 8 11:17:26 2015 -0700

    fix so that it works on linux (at least on my system)

diff --git a/build.py b/build.py
index 5f2a741..af91483 100644
--- a/build.py
+++ b/build.py
@@ -94,7 +94,11 @@ def minify(inlibs, inlibs_nomin, outlib):
     if True: # minify if True
         env = os.environ.copy()
         env["NODE_PATH"] = "build-tools/UglifyJS"
-        uglify = subprocess.Popen( "build-tools/node.exe build-tools/UglifyJS/bin/uglifyjs",
+        nodeprog = '/usr/bin/nodejs'            # linux
+        if not os.path.isfile(nodeprog):
+          nodeprog = './build-tools/node.exe'   # windows
+        uglify = subprocess.Popen([nodeprog,
+                "build-tools/UglifyJS/bin/uglifyjs"],
             stdin=subprocess.PIPE,
             stdout=outf,
             env=env