Bug#1001770: libgmsh4.8: needs Breaks+Replaces: libgmsh4 (>= 4.8)

[Andreas Beckmann]

Followup-For: Bug #1001770
Control: reassign -1 libgmsh4.8 4.8.4+ds1-1
Control: retitle -1 libgmsh4.8: needs Breaks+Replaces: libgmsh4 (>= 4.8)

libgmsh4.8 is the new package and co-installable with libgmsh4 4.7.* in
stable, thus the a bit unusual (>= 4.8) relation to only break the bad
version in sid.

Andreas