Skipping spaces in configuration files (ticket #1557).

Skipping spaces in configuration files (ticket #1557).

Previously, a chunk of spaces larger than NGX_CONF_BUFFER (4096 bytes)
resulted in the "too long parameter" error during parsing such a
configuration.  This was because the code only set start and start_line
on non-whitespace characters, and hence adjacent whitespace characters
were preserved when reading additional data from the configuration file.
Fix is to always move start and start_line if the last character was
a space.