droplet: url encoding homogeneity
first try...
 fix wrong test on path_len (leads to '/' being incorrectly detected as regular file)
 fix listing in S3 backend: skip heading slashes because S3 prefixes have no heading slash
 droplet: check string length in dpl_cwd()
 droplet: libdroplet errors in header file
 droplet: limits on path length are not fs-friendly

We set the max path length to 4096 instead of 1024.
We also change the header size to 8192 by default (instead of 1024...). You can change it
in your profile file, with 'header_size = XXX', or export DPL_HEADER_SIZE=XXX
 droplet: prefix the exported symbol with dpl to avoid pollution

 - also, remove the env variable DPL_HEADER_SIZE
Merge pull request #132 from scality/scality_svn

Scality svn