Enable support for release candidate builds

Building release candidates helps test the upstream code before it's
final.  Make it easier to create such builds by defining an rcrev macro,
which is commented out by default.

git.spec

@@ -56,15 +56,18 @@
 %global make_test_opts -O %{?_smp_mflags}
 %endif
 
+# Define for release candidates
+#global rcrev   .rc0
+
 Name:           git
 Version:        2.15.0
-Release:        2%{?dist}
+Release:        2%{?rcrev}%{?dist}
 Summary:        Fast Version Control System
 License:        GPLv2
 Group:          Development/Tools
 URL:            https://git-scm.com/
-Source0:        https://www.kernel.org/pub/software/scm/git/%{name}-%{version}.tar.xz
-Source1:        https://www.kernel.org/pub/software/scm/git/%{name}-%{version}.tar.sign
+Source0:        https://www.kernel.org/pub/software/scm/git/%{?rcrev:testing/}%{name}-%{version}%{?rcrev}.tar.xz
+Source1:        https://www.kernel.org/pub/software/scm/git/%{?rcrev:testing/}%{name}-%{version}%{?rcrev}.tar.sign
 
 # Junio C Hamano's key is used to sign git releases, it can be found in the
 # junio-gpg-pub tag within git.
@@ -381,7 +384,7 @@ xz -dc $src > $tar
 gpgv2 --homedir "$gpghome" --quiet --keyring $key.gpg $tar.sign $tar
 rm -rf "$tar" "$gpghome" # Cleanup tar files and tmp gpg home dir
 
-%setup -q
+%setup -q -n %{name}-%{version}%{?rcrev}
 %patch0 -p1
 %patch1 -p1
 %patch2 -p1
@@ -797,6 +800,7 @@ rm -rf %{buildroot}
 %changelog
 * Tue Nov 21 2017 Todd Zullinger <tmz@pobox.com>
 - Add tcl/tk BuildRequires
+- Enable support for release candidate builds
 
 * Tue Nov 07 2017 Todd Zullinger <tmz@pobox.com> - 2.15.0-2
 - Fix git-clone memory exhaustion (CVE-2017-15298)