[devtools] Use git pretty-format for year parsing

contrib/devtools/fix-copyright-headers.py

@@ -16,7 +16,7 @@
 import re
 
 year = time.gmtime()[0]
-CMD_GIT_DATE = "git log %s | grep Date | head -n 1"
+CMD_GIT_DATE = 'git log --format=@%%at -1 %s | date +"%%Y" -u -f -'
 CMD_REGEX= "perl -pi -e 's/(20\d\d)(?:-20\d\d)? The Bitcoin/$1-%s The Bitcoin/' %s"
 REGEX_CURRENT= re.compile("%s The Bitcoin" % year)
 CMD_LIST_FILES= "find %s | grep %s"
@@ -38,7 +38,7 @@ def get_git_date(file_path):
       file_path = os.getcwd() + file_path[1:-1]
       if file_path.endswith(extension):
         git_date = get_git_date(file_path)
-        if len(git_date) > 0 and str(year) in git_date:
+        if str(year) == git_date:
           # Only update if current year is not found
           if REGEX_CURRENT.search(open(file_path, "r").read()) is None:
             print n,"Last git edit", git_date, "-", file_path