Update libgit2 to 0.27

Hello everyone,

0.27.x is released long time ago, but I never got time for updating it. It
obviously involves SONAME change.

The good thing about this release is that it breaks only things in runtime
and only one function changed signature (for building) which nobody uses

I'm going to update library as soon as I get time (possibly on this weekend
if no all dependent packages build fine). I will handle all rebuilds
myself, just sending a notice.

List of affected packages is below.
Maintainers by package:
R-git2r qulogic
geany-plugins dmaphy ohaessler pingou
ghc-bdcs-api clumens
ghc-gi-ggit dshea
git-evtag ignatenkobrain walters
gitg ankursinha ignatenkobrain nacho pwalter
julia nalimilan
kf5-ktexteditor dvratil jgrulich rdieter than
libgit2-glib ignatenkobrain kalev nacho pwalter
python-pygit2 pwalter
rubygem-rugged ignatenkobrain ktdreyer tdawson
rust-exa ignatenkobrain
rust-pretty-git-prompt ignatenkobrain ttomecek
subsurface pingou

Packages by maintainer:
ankursinha gitg
clumens ghc-bdcs-api
dmaphy geany-plugins
dshea ghc-gi-ggit
dvratil kf5-ktexteditor
ignatenkobrain git-evtag gitg libgit2-glib rubygem-rugged rust-exa
jgrulich kf5-ktexteditor
kalev libgit2-glib
ktdreyer rubygem-rugged
nacho gitg libgit2-glib
nalimilan julia
ohaessler geany-plugins
pingou geany-plugins subsurface
pwalter gitg libgit2-glib python-pygit2
qulogic R-git2r
rdieter kf5-ktexteditor
tdawson rubygem-rugged
than kf5-ktexteditor
ttomecek rust-pretty-git-prompt
walters git-evtag