os: rename tmpDir() to tmpdir() for consistency

Make the casing consistent with the other os.* functions but keep
os.tmpDir() around as an alias.

doc/api/os.markdown

@@ -6,7 +6,7 @@ Provides a few basic operating-system related utility functions.
 
 Use `require('os')` to access this module.
 
-## os.tmpDir()
+## os.tmpdir()
 
 Returns the operating system's default directory for temp files.
 

lib/os.js

@@ -41,13 +41,15 @@ exports.platform = function() {
   return process.platform;
 };
 
-exports.tmpDir = function() {
+exports.tmpdir = function() {
   return process.env.TMPDIR ||
          process.env.TMP ||
          process.env.TEMP ||
          (process.platform === 'win32' ? 'c:\\windows\\temp' : '/tmp');
 };
 
+exports.tmpDir = exports.tmpdir;
+
 exports.getNetworkInterfaces = util.deprecate(function() {
   return exports.networkInterfaces();
 }, 'getNetworkInterfaces is now called `os.networkInterfaces`.');

test/simple/test-os.js

@@ -31,13 +31,13 @@ process.env.TMPDIR = '/tmpdir';
 process.env.TMP = '/tmp';
 process.env.TEMP = '/temp';
 var t = ( process.platform === 'win32' ? 'c:\\windows\\temp' : '/tmp' );
-assert.equal(os.tmpDir(), '/tmpdir');
+assert.equal(os.tmpdir(), '/tmpdir');
 process.env.TMPDIR = '';
-assert.equal(os.tmpDir(), '/tmp');
+assert.equal(os.tmpdir(), '/tmp');
 process.env.TMP = '';
-assert.equal(os.tmpDir(), '/temp');
+assert.equal(os.tmpdir(), '/temp');
 process.env.TEMP = '';
-assert.equal(os.tmpDir(), t);
+assert.equal(os.tmpdir(), t);
 
 var endianness = os.endianness();
 console.log('endianness = %s', endianness);