Former Whitpain Township police officer Gerald Schwartz has been acquitted of all charges stemming from a drunk driving arrest and an alleged physical altercation with his wife while he was off duty in Whitemarsh Township almost a year and a half ago.   During the trial, an attorney for the 47-year-old Philadelphia resident argued there was insufficient evidence to convict Schwartz.   His wife, the alleged target of the violence, did not testify against her husband.