build: change the fallback version suffix to `+git.{sha}`

Seems to be more commonly used than the current `-commit-{sha}`.
Also cleanup/simplify the version handling code.

Change-Id: I551c78632037c7156319b7ff7a327980f73ce265
diff --git a/.gitignore b/.gitignore
index 8850587..dc40a00 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,20 @@
-# Emacs
+# Backup files
 *~
+*.bak
+*.orig
+*.rej
+
+# Waf build system
+/build/
+.waf-*-*/
+.waf3-*-*/
+.lock-waf*
+
+# Compiled python code
+__pycache__/
+*.py[cod]
+
+# Emacs
 \#*\#
 /.emacs.desktop
 /.emacs.desktop.lock
@@ -15,15 +30,5 @@
 .LSOverride
 ._*
 
-# Waf build system
-/build/
-.waf-*-*/
-.waf3-*-*/
-.lock-waf*
-
-# Compiled python code
-__pycache__/
-*.py[cod]
-
 # Other
 /VERSION.info