swift234

Fix <rdar://problem/21080671> QoI: try/catch (instead of do/catch) creates silly diagnostics

People will keep typing try/catch either due to muscle memory from other languages or
when they are first learning swift.  We now produce a nice error message + fixit of:

t.swift:14:3: error: the 'do' keyword is used to specify a 'catch' region
  try {
  ^~~
  do

instead of spewing out:

t.swift:15:4: error: consecutive statements on a line must be separated by ';'
  } catch { }
   ^
   ;
t.swift:15:5: error: expected expression
  } catch { }
    ^
t.swift:15:11: error: braced block of statements is an unused closure
  } catch { }
          ^
t.swift:14:7: error: expression resolves to an unused function
  try {
  ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
t.swift:15:11: error: expression resolves to an unused function
  } catch { }
          ^~~
t.swift:14:3: warning: no calls to throwing functions occur within 'try' expression
  try {
  ^