The L293 datasheet says external clamp diodes are required for inductive loads...
The L293D has inbuilt diodes. I'm still trying to figure out how he got the motor to work with just the logic hooked up but if the logic supply was also supplying the motor then that and the voltage drop thru the regulator would make it a little toasty. I like to put weak pulldowns on the enables and also run a ground wire (like a servo) with the wires for the control signals so as to form the common ground. About the only reason to have the 7805 would be to use the motor voltage for the logic without having to supply another voltage that needs to be regulated. The arduino should easily supply the +5 for the L293D.
The L293D is plugged in backwards. Look at the notch orientation on the board file (to the right) and look at it on your board (to the left).
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