Several changes, see commit details.

[froloffw7]

Changes

1. In function do_create() change 'a' open mode to 'wb', as 'a' doesn't support unbuffered operation, and "ab" doesn't allow file shrink, only enlarge.

2. Do not create remote file in dry-run mode ('--createdest' option).

3. Server return negative size if remote file doesn't exists. Worker check received value and show error message if it is negative.

4. Send file name and blocksize with separate print(), as filename could contain spaces, so split with not work correct way.

5. Enquote path.

6. Change default ciphering to 'aes128-ctr'. Probably we can just drop that option flag, if cipher is not specified.

7. Change '--compress' option to '--nocompress', as there was no way to switch compression off, which cause significant speed degradation on local network.

[guppy]

Could we get this committed? All these changes are sane.