gnu: Add markdown.

* gnu/packages/textutils.scm (markdown): New variable.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

substitute: Increase TTL from 24h to 36h.

* guix/scripts/substitute.scm (%narinfo-ttl): Increase to 36h.

gnu: Add libwpg.

* gnu/packages/libreoffice.scm (libwpg): New variable.

guix: build: Fix indentation for --sources in help output.

* guix/scripts/build.scm (show-help)[--sources]: Make indentation
  consistent with other long options.

gnu: curl: Update to 7.42.1.

* gnu/packages/patches/curl-support-capath-on-gnutls-conf.patch,
  gnu/packages/patches/curl-support-capath-on-gnutls.patch: Remove files.
* gnu-system.am (dist_patch_DATA): Remove them.
* gnu/packages/curl.scm (curl): Update to 7.42.1.  Remove patches.

gnu: Add python-sympy.

* gnu/packages/python.scm (python-sympy, python2-sympy): New variables.

doc: Fix dangling references in the 'sh-symlink' monad example.

Reported by Christopher A. Webber <cwebber@dustycloud.org>.

* doc/guix.texi (The Store Monad): Reintroduce 'mlet' in 'sh-symlink'
  example.  Move the simplified version below.  Explain that the 'store'
  parameter is threaded.

doc: Suggest 'groupadd --system'.

* doc/guix.texi (Build Environment Setup): Use 'groupadd --system'.

doc: Clarify installation from the binary tarball.

* doc/guix.texi (Binary Installation): Specifically refer to
  group/account creation, and add an item for substitutes.  Mention
  verifiability.

gnu: bamtools: Set rpath via LDFLAGS.

* gnu/packages/bioinformatics.scm (bamtools): Add a pre-configure phase
  setting $LDFLAGS to set the rpath to $out/lib/bamtools.

gnu: Add taskwarrior.

* gnu/packages/task-management.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.

gnu: Add samtools-0.1.19.

* gnu/packages/bioinformatics.scm (samtools-0.1): New variable.

gnu: samtools: Install libbam.a library.

* gnu/packages/bioinformatics.scm (samtools)[arguments]: Add phase
  "install-library" to install the libbam.a library.

gnu: samtools: Remove patch-makefile-curses phase.

* gnu/packages/bioinformatics.scm (samtools)[arguments]: Remove
  patch-makefile-curses phase, use make-flags instead.

gnu: gcc-5.1: Add specific libvtv patch.

* gnu/packages/patches/gcc-5.0-libvtv-runpath.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/gcc.scm (gcc-5.1)[source]: Use it.

guix package: Introduce 'evaluate-search-paths'.

* guix/scripts/package.scm (evaluate-search-paths): New procedure, with
  most of the code formerly in 'search-path-environment-variables'.
  (search-path-environment-variables): Use it.

guix package: Move profile cleaning out of 'search-path-environment-variables'.

* guix/scripts/package.scm (user-friendly-profile): New procedure.
  (search-path-environment-variables): Remove 'profile' local variable.
  (display-search-paths): Explicitly call 'user-friendly-profile' for
  the argument to 'search-path-environment-variables'.
  (guix-package)[process-query]: Likewise.

gnu: Add totem-pl-parser.

* gnu/packages/gnome.scm (totem-pl-parser): New variable.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

doc: Replace reference to profile.sh with sh-symlink

* doc/guix.texi (The Store Monad): Replace reference to "profile.sh",
  which is not defined until the next node, with "sh-symlink", which
  is defined immediately above

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu: Add libe-book.

* gnu/packages/libreoffice.scm (libe-book): New variable.

Co-authored-by: John Darrington <jmd@gnu.org>