New upstream release 1.7.3
    
    - https://github.com/less/less.js/blob/v1.7.1/CHANGELOG.md
    - Fix detection of recursive mixins
    - Fix the paths option for later versions of node (0.10+)
    - Fix paths joining bug
    - Fix a number precision issue on some versions of node
    - Fix an IE8 issue with importing css files
    - Fix IE11 detection for xhr requests
    - Modify var works if the last line of a less file is a comment.
    - Better detection of valid hex colour codes
    - Some stability fixes to support a low number of available file handles
    - Support comparing values with different quote types e.g.
      "test" now === 'test'
    - Give better error messages if accessing a url that returns a non 200 status
      code
    - Fix the e() function when passed empty string
    - Several minor bug fixes
    - https://github.com/less/less.js/blob/v1.7.2/CHANGELOG.md
    - Allow paths option to be a string (in 1.7.1 less started throwing an
      exception instead of incorrectly processing the string as an array of chars)
    - Do not round numbers when used with javascript (introduced 1.7.0)
    - https://github.com/less/less.js/blob/v1.7.3/CHANGELOG.md
    - Do not round the results of color functions, like lightness, hue, luma etc.
    - Support cover and contain keywords in background definitions