Makefile nice err msg if no Node or installed wrong

In response to this today:
https://mathquill.slack.com/archives/mathquill/p1458182072000301

Holy *shitsnacks* I forgot how much Make sucks. I literally can't quote
my argument to the `ifneq` conditional.

And of course, I'm writing this to workaround the fucking Debian package
repo maintainers...

Makefile

diff --git a/Makefile b/Makefile
index 39df479..7ce1207 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,23 @@
 #
+# -*- Prerequisites -*-
+#
+
+# the fact that 'I am Node.js' is unquoted here looks wrong to me but it
+# CAN'T be quoted, I tried. Apparently in GNU Makefiles, in the paren+comma
+# syntax for conditionals, quotes are literal; and because the $(shell...)
+# call has parentheses and single and double quotes, the quoted syntaxes
+# don't work (I tried), we HAVE to use the paren+comma syntax
+ifneq ($(shell node -e 'console.log("I am Node.js")'), I am Node.js)
+  ifeq ($(shell nodejs -e 'console.log("I am Node.js")' 2>/dev/null), I am Node.js)
+    $(error You have /usr/bin/nodejs but no /usr/bin/node, please 'sudo apt-get install nodejs-legacy' (see http://stackoverflow.com/a/21171188/362030 ))
+  endif
+
+  $(error Please install Node.js: https://nodejs.org/ )
+endif
+
+
+
+#
 # -*- Configuration -*-
 #