gnu: fltk: Fix undefined symbol errors for shared libraries.

* gnu/packages/patches/fltk-shared-lib-defines.patch: New patch.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/fltk.scm (source)[patches]: New field.

gnu: ardour: Add library dirs to RUNPATH.

* gnu/packages/audio.scm (ardour)[arguments]: Add a build phase to add all
  library output directories to the rpath using linker flags.

gnu: Add bluez.

* gnu/packages/linux.scm (bluez): New variable.

gnu: Add libical.

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

gnu: Add soil.

* gnu/packages/gl.scm (soil): New variable.

records: Make 'make-syntactic-constructor' available at load/eval/expand.

* guix/records.scm (make-syntactic-constructor): Wrap in 'eval-when'.

profiles: Use a &message error condition instead of 'error'.

* guix/profiles.scm (sexp->manifest): Use 'raise' instead of 'error'.

search-paths: 'evaluate-search-paths' now returns spec/value pairs.

* guix/search-paths.scm (evaluate-search-paths): Return
  specification/value pairs instead of variable/value pairs.
* guix/scripts/package.scm (search-path-environment-variables): Adjust
  accordingly.  Pass #:separator to 'environment-variable-definition'.

search-paths: Add 'environment-variable-definition'.

* guix/search-paths.scm (environment-variable-definition): New variable.
* guix/scripts/package.scm (search-path-environment-variables): Use it.

search-paths: Add 'evaluate-search-paths', from (guix scripts package).

* guix/scripts/package.scm (with-null-error-port,
  evaluate-search-paths): Move to...
* guix/search-paths.scm: ... here.
* guix/utils.scm (string-tokenize*): Move to...
* guix/search-paths.scm: ... here.
* tests/utils.scm ("string-tokenize*"): Adjust accordingly.

Move search path specifications to (guix search-paths).

* guix/packages.scm (<search-path-specification>,
  search-path-specification->sexp, sexp->search-path-specification):
  Move to...
* guix/search-paths.scm: ... here.  New file.
* Makefile.am (MODULES): Add it.
* guix/build-system/cmake.scm, guix/build-system/glib-or-gtk.scm,
  guix/build-system/gnu.scm, guix/build-system/haskell.scm,
  guix/build-system/perl.scm, guix/build-system/python.scm,
  guix/build-system/ruby.scm, guix/build-system/waf.scm,
  guix/profiles.scm, guix/scripts/package.scm: Use it.

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.