use git version information if possible, otherwise use information

from (I3_)VERSION files (for tarballs)

common.mk

@@ -18,12 +18,14 @@ ifndef SYSCONFDIR
   endif
 endif
 
-# In dist tarballs, the version is stored in the I3_VERSION and VERSION files.
-I3_VERSION := '$(shell [ -f $(TOPDIR)/I3_VERSION ] && cat $(TOPDIR)/I3_VERSION)'
-VERSION := '$(shell [ -f $(TOPDIR)/VERSION ] && cat $(TOPDIR)/VERSION)'
-ifeq ('',$(I3_VERSION))
-VERSION := $(shell git describe --tags --abbrev=0)
-I3_VERSION := '$(shell git describe --tags --always) ($(shell git log --pretty=format:%cd --date=short -n1), branch \"$(shell git describe --tags --always --all | sed s:heads/::)\")'
+# In dist and snapshot tarballs, use the I3_VERSION and VERSION files. Otherwise use git information.
+ifeq ($(wildcard .git),)
+  # not in git repository
+  VERSION := '$(shell [ -f $(TOPDIR)/VERSION ] && cat $(TOPDIR)/VERSION)'
+  I3_VERSION := '$(shell [ -f $(TOPDIR)/I3_VERSION ] && cat $(TOPDIR)/I3_VERSION)'
+else
+  VERSION := $(shell git describe --tags --abbrev=0)
+  I3_VERSION := '$(shell git describe --tags --always) ($(shell git log --pretty=format:%cd --date=short -n1), branch \"$(shell git describe --tags --always --all | sed s:heads/::)\")'
 endif
 
 MAJOR_VERSION := $(shell echo ${VERSION} | cut -d '.' -f 1)