### Please describe the problem.

When using tab-completion for git-annex subcommands, filenames with spaces (or other special characters) are not correctly handled.

### What steps will reproduce the problem?

[[!format sh """
$ touch 'foo bar.baz'
$ git annex 'foo<tab>  # completes to 'foo bar.baz', as expected
$ git annex add 'foo<tab>  # presents the following (incorrect) options
bar.baz  foo
"""]]

### What version of git-annex are you using? On what operating system?

[[!format sh """
$ git annex version
git-annex version: 6.20180719
build flags: Assistant Webapp Pairing S3(multipartupload)(storageclasses) WebDAV Inotify ConcurrentOutput Feeds Testsuite
dependency versions: aws-0.20 bloomfilter-2.0.1.0 cryptonite-0.25 DAV-1.3.2 feed-1.0.0.0 ghc-8.4.3 http-client-0.5.13.1 persistent-sqlite-2.8.1.2 uuid-1.3.13 yesod-1.6.0
key/value backends: SHA256E SHA256 SHA512E SHA512 SHA224E SHA224 SHA384E SHA384 SHA3_256E SHA3_256 SHA3_512E SHA3_512 SHA3_224E SHA3_224 SHA3_384E SHA3_384 
SKEIN256E SKEIN256 SKEIN512E SKEIN512 BLAKE2B256E BLAKE2B256 BLAKE2B512E BLAKE2B512 BLAKE2B160E BLAKE2B160 BLAKE2B224E BLAKE2B224 BLAKE2B384E BLAKE2B384 
BLAKE2S256E BLAKE2S256 BLAKE2S160E BLAKE2S160 BLAKE2S224E BLAKE2S224 BLAKE2SP256E BLAKE2SP256 BLAKE2SP224E BLAKE2SP224 SHA1E SHA1 MD5E MD5 WORM URL
remote types: git gcrypt p2p S3 bup directory rsync web bittorrent webdav adb tahoe glacier ddar hook external
operating system: linux x86_64
supported repository versions: 3 5 6
upgrade supported from repository versions: 0 1 2 3 4 5
"""]]

### Please provide any additional information below.

This is a one-line patch that *somewhat* fixes the issue:

[[!format sh """
--- a/bash-completion.bash
+++ b/bash-completion.bash
@@ -20,6 +20,7 @@ complete -o bashdefault -o default -o filenames -F _git-annex git-annex
 _git_annex() {
     local cmdline
     CMDLINE=(--bash-completion-index $(($COMP_CWORD - 1)))
+    local IFS=$'\n'

     local seen_g`
"""]]

I've certainly not tested this thoroughly, but the problem demonstrated above is fixed, and a cursory check of other commands seems to behave as expected.

However, it doesn't correctly handle escape characters. Typically, a filename completion escapes special characters as needed, taking into account quoting rules if necessary. This one line patch doesn't seem to do that and completes to names with raw spaces.

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Many times over! I use git-annex to manage my hundreds of pdfs, images, video files etc! It essentially enables *exactly* the work flow I like, since I live in the command line and appreciate fine-grained control over my tools. So, yes, thank you very much for this excellent too!

> [[fixed|done]] --[[Joey]]
