Reimplement ChordRepetition facility.

input/regression/tablature-chord-repetition-finger.ly

+\version "2.15.28"
+
+\header {
+  texidoc = "In a TabStaff, the chord repetition function needs
+to retain string and fingering information.  Using
+@code{\\tabChordRepeats} achieves that, in contrast to the music
+on the main staff."
+}
+
+Guitar = \relative c' {
+  r8 < gis-6 cis-6 b-0 > ~ q4 q8 ~ q q4
+}
+
+\score {
+  \new StaffGroup <<
+    \new Staff {
+      \new Voice {
+        \clef "treble_8"
+        \Guitar
+      }
+    }
+    \new TabStaff {
+      \new TabVoice {
+        \tabChordRepeats \Guitar
+      }
+    }
+  >>
+}