Rising enrollments and tight revenues are putting a squeeze on the Maine Community College System.  MCCS officials say applications are up 20 percent system-wide, and on some campuses the increase is even more dramatic.  Applications at Kennebec Valley Community College in Fairfield have shot up nearly 40 percent, officials say.  They attribute the increases to the weak economy and rising unemployment.   President John Fitzsimmons says enrollment in the Maine Community College System has risen by more than 60 percent since MCCS was founded in 2003.  But during that time, Fitzsimmons says, state funding has become tight.  He says the system has been forced to confront a $2.9 million curtailment in its appropriation for the fiscal year that ends in June.  He says the MCCS is being stretched too thin, and will not be able to serve all of those who have applied.