Eliminate floating point arithmatic in nre

Integer division is already hard enough on your CPU, using floating
point here is WAY slower and can just as effectivly be done using
integers. This is important because matchImpl tends to be in the center
of very hot loops (like split()).

(cherry picked from commit 9ca1c2c930)

lib/impure/nre.nim

@@ -469,7 +469,8 @@ proc matchImpl(str: string, pattern: Regex, start, endpos: int, flags: int): Opt
   # 1x capture count as slack space for PCRE
   let vecsize = (pattern.captureCount() + 1) * 3
   # div 2 because each element is 2 cints long
-  myResult.pcreMatchBounds = newSeq[HSlice[cint, cint]](ceil(vecsize / 2).int)
+  # plus 1 because we need the ceiling, not the floor
+  myResult.pcreMatchBounds = newSeq[HSlice[cint, cint]]((vecsize div 2) + 1)
   myResult.pcreMatchBounds.setLen(vecsize div 3)
 
   let strlen = if endpos == int.high: str.len else: endpos+1