Canonicalize symlinked paths to rbenv executable

[devstuff]

Problem:

If rbenv-doctor is downloaded and installed locally (in the PATH), running rbenv doctor results in a warning:

Checking for `rbenv' in PATH: multiple
  You seem to have multiple rbenv installs in the following locations.
  Please pick just one installation and remove the others.
  
  /usr/local/Cellar/rbenv/1.2.0/libexec/rbenv
  /usr/local/bin/rbenv

The Homebrew installation has /usr/local/bin/rbenv symlinked to /usr/local/Cellar/rbenv/1.2.0/libexec/rbenv.

Fix:

Canonicalizing symlinks results in a single canonical path:

Checking for `rbenv' in PATH: /usr/local/Cellar/rbenv/1.2.0/libexec/rbenv

NOTE:

Running the command directly via curl, as per the README, results in a single path:

Checking for `rbenv' in PATH: /usr/local/bin/rbenv

Running the command directly as /some/path/rbenv-doctor results in a single path. When launched via rbenv is when the multiple paths are detected.

I assume this discrepancy may be related to my environment, but the canonicalized path is the correct result.