exchange: refactor APIs to obtain bundle data (API) Currently, exchange.getbundle() returns either a cg1unpacker or a util.chunkbuffer (in the case of bundle2). This is kinda OK, as both expose a .read() to consumers. However, localpeer.getbundle() has code inferring what the response type is based on arguments and converts the util.chunkbuffer returned in the bundle2 case to a bundle2.unbundle20 instance. This is a sign that the API for exchange.getbundle() is not ideal because it doesn't consistently return an "unbundler" instance. In addition, unbundlers mask the fact that there is an underlying generator of changegroup data. In both cg1 and bundle2, this generator is being fed into a util.chunkbuffer so it can be re-exposed as a file object. util.chunkbuffer is a nice abstraction. However, it should only be used "at the edges." This is because keeping data as a generator is more efficient than converting it to a chunkbuffer, especially if we convert that chunkbuffer back to a generator (as is the case in some code paths currently). This patch refactors exchange.getbundle() into exchange.getbundlechunks(). The new API returns an iterator of chunks instead of a file-like object. Callers of exchange.getbundle() have been updated to use the new API. There is a minor change of behavior in test-getbundle.t. This is because `hg debuggetbundle` isn't defining bundlecaps. As a result, a cg1 data stream and unpacker is being produced. This is getting fed into a new bundle20 instance via bundle2.writebundle(), which uses a backchannel mechanism between changegroup generation to add the "nbchanges" part parameter. I never liked this backchannel mechanism and I plan to remove it someday. `hg bundle` still produces the "nbchanges" part parameter, so there should be no user-visible change of behavior. I consider this "regression" a bug in `hg debuggetbundle`. And that bug is captured by an existing "TODO" in the code to use bundle2 capabilities.

DOCUMENT_ROOT="/var/www/hg"; export DOCUMENT_ROOT
GATEWAY_INTERFACE="CGI/1.1"; export GATEWAY_INTERFACE
HTTP_ACCEPT="text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5"; export HTTP_ACCEPT
HTTP_ACCEPT_CHARSET="ISO-8859-1,utf-8;q=0.7,*;q=0.7"; export HTTP_ACCEPT_CHARSET
HTTP_ACCEPT_ENCODING="gzip,deflate"; export HTTP_ACCEPT_ENCODING
HTTP_ACCEPT_LANGUAGE="en-us,en;q=0.5"; export HTTP_ACCEPT_LANGUAGE
HTTP_CACHE_CONTROL="max-age=0"; export HTTP_CACHE_CONTROL
HTTP_CONNECTION="keep-alive"; export HTTP_CONNECTION
HTTP_HOST="hg.omnifarious.org"; export HTTP_HOST
HTTP_KEEP_ALIVE="300"; export HTTP_KEEP_ALIVE
HTTP_USER_AGENT="Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.8.0.4) Gecko/20060608 Ubuntu/dapper-security Firefox/1.5.0.4"; export HTTP_USER_AGENT
PATH_INFO="/"; export PATH_INFO
PATH_TRANSLATED="/var/www/hg/index.html"; export PATH_TRANSLATED
QUERY_STRING=""; export QUERY_STRING
REMOTE_ADDR="127.0.0.2"; export REMOTE_ADDR
REMOTE_PORT="44703"; export REMOTE_PORT
REQUEST_METHOD="GET"; export REQUEST_METHOD
REQUEST_URI="/test/"; export REQUEST_URI
SCRIPT_FILENAME="/home/hopper/hg_public/test.cgi"; export SCRIPT_FILENAME
SCRIPT_NAME="/test"; export SCRIPT_NAME
SCRIPT_URI="http://hg.omnifarious.org/test/"; export SCRIPT_URI
SCRIPT_URL="/test/"; export SCRIPT_URL
SERVER_ADDR="127.0.0.1"; export SERVER_ADDR
SERVER_ADMIN="eric@localhost"; export SERVER_ADMIN
SERVER_NAME="hg.omnifarious.org"; export SERVER_NAME
SERVER_PORT="80"; export SERVER_PORT
SERVER_PROTOCOL="HTTP/1.1"; export SERVER_PROTOCOL
SERVER_SIGNATURE="<address>Apache/2.0.53 (Fedora) Server at hg.omnifarious.org Port 80</address>"; export SERVER_SIGNATURE
SERVER_SOFTWARE="Apache/2.0.53 (Fedora)"; export SERVER_SOFTWARE