Fixes for buildinfo of exported source tree

- Better to set branch/hash to "unknown" so
  it's clear build is done from exported tree.
- SCons used to reference undefined variable.

build_files/cmake/buildinfo.cmake

@@ -3,8 +3,8 @@
 
 # Extract working copy information for SOURCE_DIR into MY_XXX variables
 # with a default in case anything fails, for examble when using git-svn
-set(MY_WC_HASH "")
-set(MY_WC_BRANCH "")
+set(MY_WC_HASH "unknown")
+set(MY_WC_BRANCH "unknown")
 set(MY_WC_COMMIT_TIMESTAMP 0)
 
 # Guess if this is a SVN working copy and then look up the revision

build_files/scons/tools/Blender.py

@@ -415,9 +415,9 @@ def buildinfo(lenv, build_type):
         build_hash = os.popen('git rev-parse --short HEAD').read().strip()
         build_branch = os.popen('git rev-parse --abbrev-ref HEAD').read().strip()
     else:
-        build_hash = ''
-        build_change = 'unknown'
-        build_branch = ''
+        build_hash = 'unknown'
+        build_commit_timestamp = '0'
+        build_branch = 'unknown'
 
     if lenv['BF_DEBUG']:
         build_type = "Debug"