rm -rf npm submodule command

Noticed today that 'npm submodule' is broken in npm 2.0.

Went digging, and thought 'Hey, how did this EVER work?'

Dug a bit deeper, and found that this command was actually let go way
back in the summer of 2013, and had been hanging around ever since due
to a glitch in the system.

So, with this patch, we've 'fixed the glitch', removing it from the set
of npm commands.

Fix npm#6369

doc/cli/npm-explore.md

@@ -32,7 +32,6 @@ The shell to run for the `npm explore` command.
 
 ## SEE ALSO
 
-* npm-submodule(1)
 * npm-folders(5)
 * npm-edit(1)
 * npm-rebuild(1)

lib/npm.js

@@ -99,7 +99,6 @@ var commandCache = {}
               , "update"
               , "outdated"
               , "prune"
-              , "submodule"
               , "pack"
               , "dedupe"
 

lib/utils/git.js

@@ -10,16 +10,20 @@ var exec = require("child_process").execFile
   , npm = require("../npm.js")
   , which = require("which")
   , git = npm.config.get("git")
+  , assert = require("assert")
+  , log = require("npmlog")
 
 function prefixGitArgs() {
   return process.platform === "win32" ? ["-c", "core.longpaths=true"] : []
 }
 
 function execGit(args, options, cb) {
+  log.info("git", args)
   return exec(git, prefixGitArgs().concat(args || []), options, cb)
 }
 
 function spawnGit(args, options, cb) {
+  log.info("git", args)
   return spawn(git, prefixGitArgs().concat(args || []), options)
 }
 
@@ -33,6 +37,7 @@ function whichGit(cb) {
 }
 
 function whichAndExec(args, options, cb) {
+  assert.equal(typeof cb, "function", "no callback provided")
   // check for git
   whichGit(function (err) {
     if (err) {