This patch implements the ideas outlined in my response to Mike Gran's
recent post entitled "Effects of updated number fixes on parsing".

In brief, it modifies scm_i_string_to_number to apply exactness
specifiers to each component _before_ calling scm_make_rectangular or
scm_make_polar, as is done in PLT Scheme.  Previously, the exactness
specifiers were applied to the complex number itself.

It also arranges for 0.0@+inf.0 and 0.0@+nan.0 to become 0.0+0.0i
instead of +nan.0+nan.0, by changing scm_c_make_polar.

Previously, all of the examples below were parsed as 0.0.
The table below shows the new behavior:

  #i0@9      : -0.0+0.0i
  #i0@+9     : -0.0+0.0i
  #i0@-9     : -0.0-0.0i
  #i0@+nan.0 :  0.0+0.0i
  #i0@+inf.0 :  0.0+0.0i
  #i0@-nan.0 :  0.0+0.0i
  #i0@-inf.0 :  0.0+0.0i

For more details, see the commit log entry.

     Best,
      Mark