tools/checkpatch.sh should check for wrongly set Executable bit

[hartmannathan]

Sometimes source files (e.g., *.c, *.h, Make.defs, etc.) are committed to the repository with the Executable bit unintentionally set (that is, file perms are stored in Git as 100755 instead of 100644).

tools/checkpatch.sh should check for this and warn if the permissions are not set properly.

Files which should be allowed executable bit:

• *.sh
• *.py
• Not sure about *.bat since these are for Windows. Does Executable bit have effect on Windows?

Note: Not recommended to use GNU Find arguments: find . -type f -executable -print because this is non-portable. POSIX Find command is: find . -type f -perm +111 -print