bug#25788: 26.0.50; first C-x C-f triggering tramp is slow

[Mark Oteiza <mvoteiza@udel.edu>]

Hi,

From -Q:

1. C-x C-f
2. Experience delay
3. C-g
4. C-x C-c

Depending on where Emacs is started, loading tramp is triggered and
there is a delay before the prompt is shown.  The delay is about a
quarter second on my system.  This is quite noticeable.

Stracing emacs started in two different directories and executing the
recipe, one log is 6884 lines, the other 1949.  The extra 5000 lines
looks like emacs is opening every library known to it, finishing up by
reading ssh/netrc/rlogin files.

In GNU Emacs 26.0.50.1 (x86_64-unknown-linux-gnu, X toolkit, Xaw scroll bars)
 of 2017-02-17 built on logos
Repository revision: 8675f9c8b8a002530d0c4e0263bb3d4cf3a649fa

Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --without-gconf --with-modules
 --with-x-toolkit=lucid 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe
 -fstack-protector-strong' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
LUCID X11 MODULES LIBSYSTEMD