debian: add less as a build dependency

For builds that run on hermetic environments, it's possible that the "less"
package is not installed by default, yet it's needed for tests to pass after
revision bf5e13e38390 (which sets less as the fallback pager).

contrib/debian/control

@@ -1,53 +1,54 b''
 Source: mercurial
 Section: vcs
 Priority: optional
 Maintainer: Mercurial Developers <[e-mail]>
 Build-Depends:
  debhelper (>= 9),
  dh-python,
+ less,
  netbase,
  python-all,
  python-all-dev,
  python-docutils,
  unzip,
  zip
 Standards-Version: 3.9.4
 X-Python-Version: >= 2.6
 
 Package: mercurial
 Depends:
  python,
  ${shlibs:Depends},
  ${misc:Depends},
  ${python:Depends},
  mercurial-common (= ${source:Version})
 Architecture: any
 Description: fast, easy to use, distributed revision control tool.
  Mercurial is a fast, lightweight Source Control Management system designed
  for efficient handling of very large distributed projects.
  .
  Its features include:
   * O(1) delta-compressed file storage and retrieval scheme
   * Complete cross-indexing of files and changesets for efficient exploration
     of project history
   * Robust SHA1-based integrity checking and append-only storage model
   * Decentralized development model with arbitrary merging between trees
   * Easy-to-use command-line interface
   * Integrated stand-alone web interface
   * Small Python codebase
 
 Package: mercurial-common
 Architecture: all
 Depends:
  ${misc:Depends},
  ${python:Depends},
 Recommends: mercurial (= ${source:Version}), ca-certificates
 Suggests: wish
 Breaks: mercurial (<< ${source:Version})
 Replaces: mercurial (<< 2.6.3)
 Description: easy-to-use, scalable distributed version control system (common files)
  Mercurial is a fast, lightweight Source Control Management system designed
  for efficient handling of very large distributed projects.
  .
  This package contains the architecture independent components of Mercurial,
  and is generally useless without the mercurial package.