Consider showing special error messages for some known errors

Show a message if Disk quota exceeded.

````
zip I/O error: Disk quota exceeded
zip error: Output file write failure (write error on zip file)
````

Memory / Timeout / 500 Errors could show message about trying database only or excluding some files. Would likely need to have improved the exclude files memory footprint.

Safe Mode issues

````
file_put_contents(): SAFE MODE Restriction in effect.  The script whose uid is 10008 is not allowed to access /var/www/vhosts/vfgcpa.com/httpdocs/wp-content/c4ca4238a0-backups owned by uid 48, /var/www/vhosts/vfgcpa.com/httpdocs/wp-content/plugins/backupwordpress/functions/core.php, 281

file_put_contents(/var/www/vhosts/vfgcpa.com/httpdocs/wp-content/c4ca4238a0-backups/index.html): failed to open stream: No such file or directory, /var/www/vhosts/vfgcpa.com/httpdocs/wp-content/plugins/backupwordpress/functions/core.php, 281

fopen(): SAFE MODE Restriction in effect.  The script whose uid is 10008 is not allowed to access /var/www/vhosts/vfgcpa.com/httpdocs/wp-content/c4ca4238a0-backups owned by uid 48, /var/www/vhosts/vfgcpa.com/httpdocs/wp-content/plugins/backupwordpress/classes/schedule.php, 580

fopen(/var/www/vhosts/vfgcpa.com/httpdocs/wp-content/c4ca4238a0-backups/.schedule-default-1-running): failed to open stream: No such file or directory, /var/www/vhosts/vfgcpa.com/httpdocs/wp-content/plugins/backupwordpress/classes/schedule.php, 580

ZipArchive::open(): SAFE MODE Restriction in effect.  The script whose uid is 10008 is not allowed to access /var/www/vhosts/vfgcpa.com/httpdocs/wp-content/c4ca4238a0-backups owned by uid 48, /var/www/vhosts/vfgcpa.com/httpdocs/wp-content/plugins/backupwordpress/hm-backup/hm-backup.php, 818PCLZIP_ERR_READ_OPEN_FAIL (-2) : Unable to open archive \'/var/www/vhosts/vfgcpa.com/httpdocs/wp-content/c4ca4238a0-backups/vfgcpa-com-default-1-complete-2013-02-18-21-52-23.zip\' in wb mode
````

MySQL Table Crash.

````
mysqldump: Got error: 144: Table \'./chamkap_wrdp2/wp_wassup\' is marked as crashed and last (automatic?) repair failed when using LOCK TABLES
````