RFR: Add tabfiles to jcheck configuration

[Magnus Ihse Bursie]

The tabfiles setting is just like the files setting, but it lists files in which tabs are allowed.

(This is to support makefiles)

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Commit messages:
 - Add tabfiles to jcheck configuration

Changes: https://git.openjdk.java.net/skara/pull/929/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=929&range=00
  Stats: 22 lines in 2 files changed: 9 ins; 7 del; 6 mod
  Patch: https://git.openjdk.java.net/skara/pull/929.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/929/head:pull/929

PR: https://git.openjdk.java.net/skara/pull/929