Fix iabs(-2147483648) bug

Issue #3 fixed.
isCorrectDouble corrected, double is now promoted to uint64_t via union.
Enchanced overflow checking for int sum, difference and product.
parseInt corrected, now it rejects empty numbers beginning with + or - or $.
maxint() dropped, INT32_MAX is now used instead.
maxreal improved to more digits.
8 jobs for master in 4 minutes and 5 seconds
Status Job ID Name Coverage
  Configure
passed #4741
mac
configure:mac

00:00:30

passed #4742
windows
configure:win32

00:00:25

 
  Build
passed #4744
mac
build:mac

00:02:30

passed #4743
windows
build:win32

00:01:52

 
  Dist
passed #4746
mac
dist:mac

00:00:22

passed #4745
windows
dist:win32

00:00:18

 
  Pack
passed #4748
mac
pack:mac

00:00:36

passed #4747
windows
pack:win32

00:00:27