Problem installing a module When I try to enable a module I get 

Fatal error: Call to undefined function modulename_cron() in /home/modulename.install on line 17 


In modulename.install I have

function modulename_install() {
  db_query('ALTER TABLE {node_revisions} ENGINE = MYISAM');
  db_query('ALTER TABLE {node_revisions} ADD FULLTEXT `similar` (`title`, `body`)');
  modulename_cron();
}


module_cron() is definitely defined in my modulename.module file. What could cause this problem and how could I fix it?
Have a look at the documentation for hook_install. It says:


  Note that functions declared in the module being installed are not yet available. The implementation of hook_install() will need to explicitly load the module before any declared functions may be invoked.