Don't allow a scheduled backup to run if it's already running in another thread. Will prevent issues where load balancers and proxies re-send requests that don't return within some arbitrary timeout period

Fixes #250
Code comments
adds function to copy settings from previous schedule
Merge pull request #284 from humanmade/fetch-destination-settings

adds function to copy settings from previous schedule
notify hipchat of build status's
Remove square brackets as they break travis.
Correct hipchat room
Don't highlight the HMBKP_TIME_CONSTANT example if it's set to the default setting as the constant is defined in the plugin
Don't allow the filesize of the site to be calculated in multiple thread at once.

Currently if the sites size is being calculated and you reload the page before the calculation has finished then another size calculation will be kicked off, on large sites this can cause issues as several requests can end up open, all calculating the size of the site.

This commit fixes that by ensuring that at a max you only get one size calculation per hour.

Fixes #229
Latest HM Backup

Fixes #208
Remove the help text for the HMBKP_EMAIL constant as it has been deprecated.
Bump for pre-release
Don't indent the copyright notice
Remove stray line break
No need to wrap hmbkp_init in a function not exists check.
Correctly calculate the HMBKP_SECURE_KEY

- Use the constant values instead of names when calculating HMBKP_SECURE_KEY
- Shuffle the array before passing to md5 as shuffle returns true rather than the shuffled array
- serialise the array before passing to md5.

Fixes #289
Don't access the hmbkp_default_path option directly as it may not be set.

Instead use hmbkp_path_default()
Re-calculate the backup path on upgrade and move any existing backups there.
Bump
Remove stray error_logs