title: conditional @import in .less or no error when file missing
body: <p>I need to conditionally import a file during a particular type of build. Using <code>grunt-contrib-jshint@0.7.0</code> which is on top of <code>less@1.4.2</code></p>
  
  <p>What I tried thus far...</p>
  
  <p>Trying to use protected mixins to determine the type of build I require and namely, to skip imports of certain less files that break in dev mode.</p>
  
  <pre><code>@isProduction: 1;
  
  ...
  
  .getImports() when (@isProduction = 1){
  }
  
  .getImports() {
      @import "productionStyles";
  }
  
  ...
  .getImports();
  </code></pre>
  
  <p>however, this seems to fail and it tries to import and parse <code>productionStyles.less</code> all the time. I guess protected mixins does not cover <code>@import</code>, so how would you solve that?</p>
  
  <p>I also tried</p>
  
  <pre><code>@productionStyles: "productionStyles"; // or 0
  
  ...
  @productionStyles: 0;
  
  
  .getImports() when not (@productionStyles = 0){
      @import "@{productionStyles}";
  }
  
  ...
  </code></pre>
  
  <p>to same avail, it will try to import it anyway <code>&gt;&gt; FileError: '0.less' wasn't found in ...</code>.</p>
  
  <p>I am starting to think it will need a bigger refactor where <code>devStyles</code> and <code>productionStyles</code> are both a thing and I just switch between them - it's just that productionStyles was an addition that can only compile after a full build due to deps and I would much rather solve this by compiling conditionally.</p>
  
  <p>I can also move away from using <code>grunt-contrib-jshint</code> and write my own less parser but would like to explore the built-in options first. </p>
  
  <p>As the <code>productionStyle.less</code> references several files that are not in the file system, is it possible to ignore the <code>@imports</code> that fail and continue building? I would prefer not to disable error checking/break on all errors due to possible parser errors elsewhere... </p>