Merge branch 'bc/more-git-var'
Add more "git var" for toolsmiths to learn various locations Git is
configured with either via the configuration or hardcoded defaults.
* bc/more-git-var:
var: add config file locations
var: add attributes files locations
attr: expose and rename accessor functions
var: adjust memory allocation for strings
var: format variable structure with C99 initializers
var: add support for listing the shell
t: add a function to check executable bit
var: mark unused parameters in git_var callbacks