fs.statSync() creates and returns a heavy-weight fs.Stat object whereas
fs.accessSync() simply returns nothing.  The return value is ignored,
the call is for its side effect of throwing an ELOOP error in case of
cyclic symbolic links.

Reduce the number of stat() system calls that require() makes by caching
the results more aggressively.

To avoid unbounded growth without implementing a LRU cache, scope the
cache to the lifetime of the first call to require().  Recursive calls
(i.e. require() calls in the included code) transparently profit from
the cache.

The benchmarked application is the loopback-sample-app[0] and it sees
the number of stat calls at start-up go down by 40%, from 4736 to 2810.

[0] https://github.com/strongloop/loopback-sample-app

Avoid an unneeded ArgumentsAdaptorTrampoline stack frame by passing the
the right number of arguments to Module._load() in Module.require().
Shortens the following stack trace with one frame:

    LazyCompile:~Module.load module.js:345
    LazyCompile:Module._load module.js:282
    Builtin:ArgumentsAdaptorTrampoline
    LazyCompile:*Module.require module.js:361
    LazyCompile:*require internal/module.js:11

Use internalModuleReadFile() to read the file from disk to avoid the
fs.fstatSync() call that fs.readFileSync() makes.

It does so to know the file size in advance so it doesn't have to
allocate O(n) buffers when reading the file from disk.

internalModuleReadFile() is plenty efficient though, even more so
because we want a string and not a buffer.  This way we also don't
allocate a buffer that immediately gets thrown away again.

This commit reduces the number of fstat() system calls in a benchmark
application[0] from 549 to 29, all made by the application itself.

[0] https://github.com/strongloop/loopback-sample-app